Just ran into the same problem.
So as a future reference, this is how you fix it:
You add a pointer to the DLL in the Registry like this:
[HKEY_CURRENT_USER\SOFTWARE\Microsoft\.NETFramework\AssemblyFolders\MyAssemblies]@="C:\\MyAssemblies"
Normally this should have been done automatically by Oracles installer, but if you install things in the wrong order this doesn't happen.
More info on the subject
here[
^].