Contribute changes the file permissions on upload to include group write.
This conflicts with the security settings allowed by the php installation on the uvic server (for good reason). The group-write permission is what generates the internal server error.
Greg and I looked up the adobe knowledgebase, where we found some information that we could get a sysadim to change settings for the account for the umask, and Contribute "would respect" those settings. Even if true, not what I want to do, so decided on php with included htms for editable bits.