InfoPath Dev

Can you post your code you added?  This error is generally a problem with data of type DateTime, Whole Number, etc.. that are not valid when left blank without the xsi:nil attribute set to "true".

Unfortunately this has been a long standing limitation which I don't think has a solution.  http://www.infopathdev.com/forums/p/1366/4560.aspx

Do the users that are initiating the workflow (when the FormState is set to complete) have permission to delete the forms from the original library? Since you know that you can initiate the workflow manually, what happens if you perform the operation to set the FormState to complete?  Does it more then? - Jim

You can create a site column in SharePoint of type Choice, and then promote the field from the InfoPath form, making sure to select your InfoPath field and then select the site column it should map to.  By checking the 'Allow users to edit data in this field by using a datasheet or properties page', the field can be edited in ...

Is the site where you are opening the InfoPath form from in your Local Intranet or Trusted sites? - Jim

I think the best way to validate in this scenario is that enforce that Document Issue Date is non-blank, and that Document Expiration Date is greater than Issue Date.    That way you don't have a two-way validation situation. Cheers - Jim

Can you provide more details on your custom validation? 

When an InfoPath form with code is pubished to SharePoint, the form's code assembly is checked that it is compatible with the Sandbox.  The checks involve reflecting over the dll and making sure no calls to restricted APIs are being made.  The QRules dll, having much more code than the simple test will take longer to ...

In SharePoint Central Administration, you need to go to General Application Settings | Manage InfoPath Form Services Make sure that "Authentication to data sources (user form templates)" is checked.

The DBXL web service uses standard SOAP protocol.   It can be called from any application that supports calling SOAP based services. It appears that SAS can call web services, but we do not have any documents specific to calling from other applications.