Too many JavaScripts doing too many unimportant things, eventually one or two of them would barf for reasons not worth looking into (incompatibility, poor code, low memory, resource contention, etc) and throw this error.
Generally you just ignore them, I just installed the NoScript plugin and hope it improves my web surfing experience.
Edited to add I had to 'allow' ibsrv.net to allow formatting of my posts.