UFL created in C#, Visual Studio .NET 2005 is not visible in the Crystal Reports Designer under the Formula Editor.
1) Ensure CR designer is not running
2) GAC the dll:
a) Copy the crufl_vb_crypto.dll into c:\program files\business objects\common\3.5\bin
b) Go to the .NET command prompt
c) Type c:\program files\business objects\common\3.5\bin gacutil -i crufl_myUFL.dll
This should give you a message; Assembly successfully added to the cache.
3) Register the UFL by the regasm.exe utility. At the .NET command prompt type:
c:\program files\business objects\common\3.5\bin regasm crufl_myUFL.dll
The Crystal Reports 2008 .NET SDK Developer Guide contains detailed information.
Also, see the blog "Creating Crystal reports User Function Libraries (UFL) with Visual Studio .NET "
UFL User Functinon Lbrary regasm gac regasm.exe NET , 3513882 , KBA , BI-RA-CR , Crystal Reports designer or Business View Manager , How To