First, go to Help>About and make sure you're running version 126.96.36.199
If not, update.
That sort of error usually means something has gone awry with a plugin. In this case, it's one of the core plugins for AE and not an odd third-party one. Thus, it usually means something is fouled up with your install. I think uninstalling and reinstalling AE may be your only solution.
Alternatively, (and I'm assuming you're on CC 2014 or version 13.2) you could try installing a different version of AE like version 12 or 11 and then copying the glow plugin from that version into the current one. However, if it's borked one thing, it's likely got issues with more than just that.
Are you sure reinstalling is the only option? cause my glow effect worked, then i installed sapphire and bcc plugins and it stopped working for some reason
Are you sure reinstalling is the only option?
No; in fact, I listed other options.