I ran into a similar problem trying to create a Data Processing Extension and finally realized that I was building my extension as a .net 4.0 dll, and ssrs only supports 3.5 (uses 2.0.50727 clr)
I refer to this thread:https://stackoverflow.com/questions/18226767/sql-server-2008-r2-reporting-service-data-processing-extension-issue
SSRS is built against the Microsoft .NET Framework 2.0 and the Microsoft .NET Framework 3.5. We recommend that you use .NET Framework 2.0 or .NET Framework 3.5 only in SSRS.
I refer to this thread:https://support.microsoft.com/en-us/topic/the-net-framework-4-x-assemblies-are-not-supported-in-sql-server-reporting-services-993895a1-4b00-9b34-f1cc-4c1f8219ccd4
Is it because of that the dll .NET version too high?
Best Regards,
Isabella
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