When i stop the server and start it back up i cant log in?

You are using an old mod the one it is throwing an error for is atlas_clothing, although there may be others. look at the error log, it says common_f is not defined, then the name of the mod.
Remove that mod, and any other mod that throws this error.

Quote

1. [ERROR] Trace:
2. ReferenceError: common_f is not defined

Not sure if it is the source of the problem, but at least you have at least 1 outdated mod that is not compatible with 1.5.1 - you need to remove it or update to compatible version if available