Have you updated the paths and urls? possible that something stale is just idling around; if you're going to purge caches via FTP you'll delete everything from templates/compile and /cache then run the content rebuilder in the Control Panel.
The UBB.threads System Requirements Test
will report quite a bit of information about your hosting environment, including your full paths.
A rule of thumb about the permissions is 666 for files, 777 for directories; however, some environments are overzealous and will not let scripts execute from a directory that's chmodded 777 (in which case you'd chmod the directory that UBB.threads is in to 755).