Custom minecraft server problem?

Okay here deal, i'm working on a custom version of the FTB monster pack, finally i was ready with the server and there seems to be no problems. But whatever a player joins the message comes Custom minecraft server problem
None of the mods adds a unlit touch, Have anybody got the same problem before?

Never heard of a problem like this. Where did you download the.exe (or.jar) from?
If you didn't download it from the official site, it may contain a virus. If i were you, i would scan your computer with an antivirus program.