I've checked the adtypes table and can confirm the id is 4.
"relook at your templates and verify they are accurate and no syntax errors"
I copied the For Sale templates which are id 0 and renamed them so that they are id 4 as in editproduct4.tmpl, showcat4.tmpl, showproduct4.tmpl & uploadproduct4.tmpl. I haven't started to edit them yet - nothing has changed within the templates yet.
Could the permissions of the files on the server maybe have any effect?