[derfelix]

I suspect the px unit is missing
ie you did not define the stylevar as Data Type size (there you can select unit ->pixel)
or you left the unit blank.
to test do following:
add px to height and width in stylesheet:

height:{vb:stylevar AJGattach_columwidth}px;
width:{vb:stylevar AJGattach_columwidth}px;

or modify the type of your stylevar...

if you are in vbullitin 4.01, change your settings to store css as files..
You can then open the stylesheet in your clientscript folder and verify what is in there..
you can also input in your browser:

http:/ /yoursite.com/forums/css.php?styleid=1&sheet=Stylesheetname.css
where Stylesheetname is the name of your stylesheet.
there you can see what your browser is seeing (ie: if it is really the px that is missing)

F.