The obvious thing to check is file and folder permissions. Both for the files you're trying to write to (css, etc.) and the modified umbraco files.
Any chance you're impersonating another user with your modifications to enable e-comm communications? If so, that might be interfering.
After these obvious checks... can you give us an error message? Look in the umbraco log. You might install Per's log viewer, available at
http://www.objects.dk/2006/6/5/log-viewer-updated.aspx, as well as adding ?umbDebugShowTrace=true to your querystring to get more details. Whatever you can provide will help.
cheers,
doug.
MVP 2007-2009 -
Percipient Studios