I’m using System.Data.OracleClient, and always get this error after install on new fresh server 64 bit.
And this how I do it to resolve:
1. Make sure your console/winform app works.
2. The resolve is just restart your PC after set 32-bit enabled on your IIS Application Pool.
Really just that restart. I try so hard that I have to copy Oracle Client dll to my \bin, but it’s not work.