So I was recording on a server and when I went to render some clips this popped up. I'd really appreciate some help

I got the same issue, i think replaymod require some mods u used while recording to be active on the client

If you have multiconnect mod, that mod is the issue

Sorry if you can't understand my comment, english isn't my main language.

Yes, so i think the best thing u can do is run with the lowest amount of mods or mods wich you know won't break Replaymod.

Due to lack of details supplied by the OP, I'll assume this was indeed caused by the multiconnect incompatibility and will close this as a duplicate of #558.