If you are having trouble uploading large documents to DBXL you might need to increase the web service timeout to allow the upload enough time to complete. This can be done on the client side with managed code, or on the server-side (which affects all Document Types) via an edit to the web.config file for the DBXL instance that is causing the problem.
Note that the web.config change noted below is intended to add the <httpRuntime> node into the system.web section, as this node does not already exist in web.config. Also note that this change is only a server-side timeout and Infopath will still timeout after 30 seconds unless you use code to set the timeout.
C#
WebServiceAdapter2 wsAdapter = (WebServiceAdapter2)thisXDocument.DataAdapters["DataConnectionName"];
wsAdapter.Timeout = 60; // Increase to 60 seconds - Default is 30
wsAdapter.Query(); // Issue the query
JScript
var wsAdapter = XDocument.DataAdapters["DataConnectionName"];
wsAdapter.Timeout = 60; // Increase to 60 seconds - Default is 30
wsAdapter.Query(); // Issue the query
web.config change
<configuration>
<system.web>
<httpRuntime executionTimeout="300"/>
</system.web>
</configuration>
Further reference