My first move would be to upload fresh files of whatever version you are currently using (taking care to not overwrite any files in the /includes, /styles, and /cache_builders/custom folders). You could have corrupted files causing the issue.
Since this isn't an issue endemic to any threads version, you can be pretty sure it's something you've done. Which means it should be fixable by uploading the unedited files - check permissions and uploading techniques (ascii vs. binary, etc.)
