Hi,
I don't know where you place your files, but did you read this? i use this method
How to Register/Unregister
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1) Build Project;
2) Copy add-in dll file to one of following locations:
a) Anywhere, then *.addin file <Assembly> setting should be updated to the full path including the dll name
(i build my dll in the project, and fill that path in de addin file)
b) Inventor <InstallPath>\bin\ folder, then *.addin file <Assembly> setting should be the dll name only: <AddInName>.dll
c) Inventor <InstallPath>\bin\XX folder, then *.addin file <Assembly> setting shoule be a relative path: XX\<AddInName>.dll
3) Copy.addin manifest file to one of following locations:
a) Inventor Version Dependent
Windows XP:
C:\Documents and Settings\All Users\Application Data\Autodesk\Inventor [version]\Addins\
Windows7/Vista:
C:\ProgramData\Autodesk\Inventor [version]\Addins\
b) Inventor Version Independent
Windows XP:
C:\Documents and Settings\All Users\Application Data\Autodesk\Inventor Addins\
Windows7/Vista:
C:\ProgramData\Autodesk\Inventor Addins\
c) Per User Override
Windows XP:
C:\Documents and Settings\<user>\Application Data\Autodesk\Inventor [version]\Addins\
Windows7/Vista:
C:\Users\<user>\AppData\Roaming\Autodesk\Inventor [version]\Addins\
4) Startup Inventor, the AddIn should be loaded
To unregister the AddIn, remove the Autodesk.<AddInName>.Inventor.addin from above mentioned .addin manifest file locations directly.
If you think this answer fullfilled your needs, improved your knowledge or leads to a solution,
please feel free to "kudos"