PC or Mac? What version of the OS?
Please list the specific steps you're trying to perform, and maybe do a screen grab and post it here showing the environment you have right as you're about to try the Save For Web operation that fails.
I have saved GIF animations from Photoshop CS6, so I know it's possible.
I don't know if it might affect Save For Web but some folks get into trouble by tying in the plug-ins from an earlier version of Photoshop. If you have copied the plug-ins folder from an older version of Photoshop, or have pointed your Extra Plug-ins Folder at the older version's plug-ins area, you will need to undo that.
i have a PC, well i made a lots of animations from ps cs5 and i never had problems with that, i just made a animation from a clip of a video like this
but when i press click photoshop crash down or this appears:
this doesn't happen to me with CS5 and i didn't copied plug-ins from another version, i just intalled it and that's all.
Maybe someone else has a suggestion. The only thing I see that seems a bit unusual is the mix of languages.
Make sure your TEMP environment variable points to a folder that your username (specifically) has Full Control access to.