mosly happened on if you're using client with encrypted Assembly-CSharp.dll and cant load the UNencrypt dll after you change the IP inside of it..
original encrypted assembly csharp:
libmono decryption call - > decrypt the assembly csharp dll ( decryp success )
after decrypt assembly csharp for editing the IP address:
libmono decryption call - > decrypt the assembly csharp dll ( decryp fail because assembly csharp already decrypt)
2 solution :
1. encrypt the dll back after editing IP
2. remove decryption call in libmono
they always said option 2 always the easier which i haven't figure that out myself