Reinstall Template, that should fix your File Catalog, everytime you install an module, like the File Catalog, then you need to reinstall Template.
Here is the <doctype> code:
Code
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
Added (08.04.2012, 12:02)
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And another thing, if you do alot of changes in Template, Remember to save the 1 you change in an Text document, so you dont have to do the changed you did over again. Ive done that so many time. 