You are looking at two different versions of the assembly.
Your code (at design/compile time) is referencing a newer version (since you're able to use TOKEN_FROM
yet when you inspect the DLL with dotPeek, it's not there). However, the assembly loaded at runtime is an older version with different underlying values thus mismatching the names.
You'll have to investigate how it is you're referencing mismatched DLLs. It could be the installed framework on the executing machine, or perhaps you have projects in the same solution referencing different versions, or perhaps some other reason (it's not possible to determine from the information you have provided).
Once you resolve why you're referencing two different versions and unify it to a single assembly version, the Enum.ToString()
result should be as you expect it.