There are two settings that could cause this to occur:
1) The symbol name is longer than the default 31 characters - you can increase the character limit in the Design Parameter under the Design Tab and look for the Long Name Size setting. (Setup > Design Parameters...)
2) The Environmental variable "no_symbol_onsave" is set in your local environment on the computer which is showing the problem. Go into the User Preferences Editor (Setup > User Preferences...) under the Drawing Category and make sure the "no_symbol_onsave" preference is not enabled. (not checked)
This assumes that there isn't something missing from your symbol (Ref Designator) or something wrong with your symbol (duplicate pin numbers or multiple shapes in one shape symbol) which would prevent the symbol from being created - but it would pop open a window to report errors in these cases.
Hope this helps,
Plexus Engineering Solutions