Here's a section from the log file that I think might be telling me what the error is... Although, I can't make any sense of it.
04/23/2013 10:55:23.20 SPUCWorkerProcess.exe (0x1B60) 0x2BBC SharePoint Foundation Sandboxed Code Service fe8s Medium - - Unhandled exception was thrown by the sandboxed code wrapper's Execute method in the partial trust app domain: An unexpected error has occurred. - userCodeWrapperType = "Microsoft.Office.InfoPath.Server.Host.FormServerUserCodeWrapper", userAssemblyGroupId = "8958EA5F802A48EBA317A9C7922ECC04-xoU7vhIi09KDniL3KzNS5BgXf6+WUQYAtKdLMrJV1OI=", siteCollectionId = "968421e1-386f-4a24-839c-016e2086977a" - Inner Exception: Microsoft.SharePoint.UserCode.SPUserCodeSolutionProxiedException: An XML error has occurred. Server stack trace: at Microsoft.Office.InfoPath.Server.Xml.SafeXmlReader.ThrowIfXmlMaxDepth() at Microsoft.Office.InfoPath.Server.Xml.SafeXmlReader.Read() at System.Xml.XmlLoader.LoadNode(Boolean skipOverWhitespace) at System.Xml.XmlLoader.LoadDocSequence(XmlDocum... f4aabf2a-f892-4607-9104-96b130daa1c6
04/23/2013 10:55:23.20* SPUCWorkerProcess.exe (0x1B60) 0x2BBC SharePoint Foundation Sandboxed Code Service fe8s Medium ...ent parentDoc) at System.Xml.XmlDocument.Load(XmlReader reader) at Microsoft.Office.InfoPath.Server.Xml.SafeXmlDocument.Load(XmlReader reader) at Microsoft.Office.InfoPath.Server.Xml.SafeXmlDocument.LoadXml(String xml) at Microsoft.Office.InfoPath.Server.DocumentLifetime.EventRichTextChange.XHTMLFixer(String xhtml) at Microsoft.Office.InfoPath.Server.DocumentLifetime.EventRichTextChange.HtmlToCleanXHtml(String html, Boolean makeDomCompatible) at Microsoft.Office.InfoPath.Server.SolutionLifetime.ItemFieldConnectorRichText.WriteValueNode(ListField fieldInformation, XmlWriter resultWriter, Object value) at Microsoft.Office.InfoPath.Server.SolutionLifetime.ItemFieldConnectorRichText.WritePropertyFromItem(Context context, ResultListItem listItem, XmlWriter resultWrit... f4aabf2a-f892-4607-9104-96b130daa1c6
04/23/2013 10:55:23.20* SPUCWorkerProcess.exe (0x1B60) 0x2BBC SharePoint Foundation Sandboxed Code Service fe8s Medium ...er, ListField fieldInformation, String itemFieldsNamespacePrefix, String itemFieldsNamespace) at Microsoft.Office.InfoPath.Server.SolutionLifetime.DataAdapterListDataProvider.PopulateXmlForMultipleItems(Context context, ResultListItemIterator listItems, Dictionary`2 existingFields, Int64& auxDomSize) at Microsoft.Office.InfoPath.Server.SolutionLifetime.DataAdapterListDataProvider.<>c__DisplayClasse.<Execute>b__3(Boolean impersonatedIdentity) at Microsoft.Office.InfoPath.Server.SolutionLifetime.DataAdapterUtil.Impersonate(DataAdapterInformation adapterInfo, String userName, String userDomain, String password, CodeToRunUnderImpersonation codeToRun) at Microsoft.Office.InfoPath.Server.SolutionLifetime.DataAdapterUtil.Impersonate(DataAdapterInformation adapterInfo, String userN... f4aabf2a-f892-4607-9104-96b130daa1c6
04/23/2013 10:55:23.20* SPUCWorkerProcess.exe (0x1B60) 0x2BBC SharePoint Foundation Sandboxed Code Service fe8s Medium ...ame, String password, CodeToRunUnderImpersonation codeToRun) at Microsoft.Office.InfoPath.Server.SolutionLifetime.DataAdapterListDataProvider.Execute(String siteUrl, Guid listId, SPContentTypeId contentTypeId, Document document, DataAdapterListDataProvider documentAdapter, Boolean useDcl, XPathNavigator queryFields, XPathNavigator resultFields, Boolean isListItemEditing, Boolean discoveryOnly, Int64& auxDomSize) at Microsoft.Office.InfoPath.Server.DocumentLifetime.DataAdapterListDataProvider.ExecuteInternal(XPathNavigator queryFields, XPathNavigator resultFields, Boolean useListItemMode) at Microsoft.Office.InfoPath.Server.DocumentLifetime.Document.QueryDataOnLoad(DataAdapter documentDataAdapter, DataObject documentDataObject) at Microsoft.Office.InfoPath.Server.DocumentLif... f4aabf2a-f892-4607-9104-96b130daa1c6
04/23/2013 10:55:23.20* SPUCWorkerProcess.exe (0x1B60) 0x2BBC SharePoint Foundation Sandboxed Code Service fe8s Medium ...etime.Document.ExecuteInitOnLoadForDataObjects() at Microsoft.Office.InfoPath.Server.DocumentLifetime.Document.LoadFromRemoteContext(Boolean firstOpened, String editingSessionId, Solution solution, Byte[] serializedState, Byte[] serializedVersionState, Dictionary`2 inputParams, OpenParameters openParameters) at Microsoft.Office.InfoPath.Server.Controls.XmlFormView..ctor(Solution solution, RemoteExecutionContext remoteExecutionContext) at Microsoft.Office.InfoPath.Server.Host.FormServerUserCodeWrapper.Execute(SPUserCodeExecutionContext executionContext) at Microsoft.SharePoint.UserCode.SPUserCodeApplicationHostAppDomainRef.ExecuteWrapper(SPUserCodeWrapper wrapper, SPUserCodeExecutionContext executionContext) at System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateP... f4aabf2a-f892-4607-9104-96b130daa1c6
04/23/2013 10:55:23.20* SPUCWorkerProcess.exe (0x1B60) 0x2BBC SharePoint Foundation Sandboxed Code Service fe8s Medium ...rocessMessage(IntPtr md, Object[] args, Object server, Int32 methodPtr, Boolean fExecuteInContext, Object[]& outArgs) at System.Runtime.Remoting.Messaging.StackBuilderSink.AsyncProcessMessage(IMessage msg, IMessageSink replySink) Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.EndInvokeHelper(Message reqMsg, Boolean bProxyCase) at System.Runtime.Remoting.Proxies.RemotingProxy.Invoke(Object NotUsed, MessageData& msgData) at Microsoft.SharePoint.UserCode.SPUserCodeApplicationHostAppDomainRef.CodeToExecuteWrapper.EndInvoke(IAsyncResult result) at Microsoft.SharePoint.UserCode.SPUserCodeApplicationHostAppDomainRef.Execute(Type userCodeWrapperType, SPUserCodeCachedAssemblyGroup userAssemblyGroup, Guid siteCollectionId, Byte[] binaryUserCodeToken, ... f4aabf2a-f892-4607-9104-96b130daa1c6
04/23/2013 10:55:23.20* SPUCWorkerProcess.exe (0x1B60) 0x2BBC SharePoint Foundation Sandboxed Code Service fe8s Medium ...Byte[] proxyOperationToken, SPUserCodeExecutionContext executionContext, Boolean shouldUsageLog, Int32 currentProcessId) f4aabf2a-f892-4607-9104-96b130daa1c6
04/23/2013 10:55:23.20 SPUCHostService.exe (0x0788) 0x0F34 SharePoint Foundation Sandboxed Code Service 0000 Medium - - An XML error has occurred. - Request executing userSolution Id "8958ea5f-802a-48eb-a317-a9c7922ecc04" for site collection id " 968421e1-386f-4a24-839c-016e2086977a" has encountered an unhandled exception while executing user code. f4aabf2a-f892-4607-9104-96b130daa1c6