You must register the .NET assemblies to the Global Assembly Cache (GAC) after the initial installation, and each time you apply a patch.
For .NET version 4:
For .NET version 2 and version 4:
To add the assemblies to the GAC, do the following:
oraprovcfg.exe/action:gac/providerpath:<assembly DLL>
For example:
oraprovcfg.exe/action:gac/providerpath:Oracle.DataAccess.dll
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