First off, next time you have an issue, I recommend creating your own thread, as that will get more views, rather than posting on a really old thread.
Second, what's the exact error that you are getting? Did you do anything that you think caused the error? For example, did you put a double quote (") in an entity keyvalue or output parameter? If you know what entity the problem is in, do CTRL-F in your text editor to find the entity class or name, then read the nearby lines to find where the improperly placed character is and delete it.
Alternatively, you can try the VMX. The VMX is effectively a backup of your VMF, except it's always a few revisions behind your VMF. To open the VMX, simply rename it and change the extension to VMF, then see if you can open it in Hammer.
The more information you provide about your problem, the easier it will be for us to help.