That error usually indicates you don’t have the DLC map installed that the server is running. When you receive that error, check the window of the external console for the following COM_ERROR, as it would indicate what I’ve mentioned:
EXE_CONFIGSTRINGMISMATCH
From FAQ & Common issues Plutonium T6:
Error: EXE_CONFIGSTRINGMISMATCH
Fix: You are either missing some DLC files or you suck at pirating, either way download some clean files.
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