[Gmod-help] Purple and Black squares and error signs

[GameAdvice4U GA4U]

When I play a downtown rp server and a few other servers, I get error sings
and purple and black squares everywhere.  The sky is also messed up too.
How do I get rid of it?  Also the guns are invisible and I just see
crosshairs when I shoot and aim.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://brie4.cshl.edu/pipermail/gmod-help/attachments/20110725/e1d5e34b/attachment.html>