what does nullreferenceexception mean in my sharepoint log - my infopath form won't “submit” anymore

Question

I tweaked my infopath form by taking out a Lookup field that i no longer needed, and deleting the Data Connection, and now i can no longer submit my form. I get this error:

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The SOAP response indicates that an error occurred on the server:

Server was unable to process request. ---> Object reference not set to an instance of an object.

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i looked in the log and found a bunch of errors - this one seems to hold a clue:

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03/07/2013 16:11:03.70* w3wp.exe (0x1670)                           0x1354  InfoPath Forms Services         Runtime                         82mk    Exception   ...lutions.<>c__DisplayClass7.<VerifyUnpackedSolution>b__6()     at Microsoft.Office.Server.Diagnostics.FirstChanceHandler.ExceptionFilter(Boolean fRethrowException, TryBlock tryBlock, FilterBlock filter, CatchBlock catchBlock, FinallyBlock finallyBlock)  7fa5fbca-2cdc-4214-afe3-eabe9b62cc69
03/07/2013 16:11:03.70  w3wp.exe (0x1670)                           0x1354  SharePoint Server               Unified Logging Service         c91s    Monitorable Watson bucket parameters: SharePoint Server 2010, ULSException14, 41b7c39f "infopath forms services", 0e00178d "14.0.6029.0", fd34ba92 "microsoft.office.infopath.server", 0e00178c "14.0.6028.0", 4dafefab "thu apr 21 01:49:47 2011", 00003708 "00003708", MISSING, 4a6d3421 "nullreferenceexception", 38326d6b "82mk"    7fa5fbca-2cdc-4214-afe3-eabe9b62cc69

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any idea what i could do to further troubleshoot this?

Answer 1

That means, that your changes are incompatible with previously published (and so hooked by sharepoint) version of the same template which is linked to previously submitted (XML, in case of library forms) data forms generated on the basis of that template.

Such incompatible changes should be made in separate (copy) of template.

Other options (your info is incomplete for qualified guess) are that:

• you made changes that are incompatible with web browser enabled forms (rendered through IPFS, Infopath Forms Services) (this link is about browser-enabled library forms but I believe it hold for sharepoint list forms also) or
• that you have not configured/enabled IPFS
• that you are not on enterprise sharepoint server while having engaged enterprise-only features
• etc.