Strange Page Not Found error at logon

Hi Everybody

I would be really grateful for some help in tracking down a 'page not found at logging in' problem. I'm using a custom theme with the php theme engine.

All users logging into the site get a 404 page not found error. The user is logged in but are directed to the error page and the Url at the 404 error reads:
http://mysite.com/sites/all/misc/menu-leaf.png

I'm not sure why the ...sites/all/misc/menu-leaf.png path should be looked for on logging in! The menu-leaf.png is not in the sites/all/misc folder but the root/misc folder.

I think the problem began when I added a css aggregation script to the template.php file which created a single css file aggregating all the site-wide css files into a single css file in the theme folder and which may account for the menu-leaf.png being looked for in the sites/all/misc folder.

I have since removed the script reverting to the former settings however the problem persist.

I tried truncating the following tables in the database but again no joy:
cache;
cache_content;
cache_filter;
cache_menu;
cache_page;
cache_views;
sessions;
watchdog;
accesslog;

Does anyone have any idea what might be causing the error, or of anything else I could try to track the problem down?

Am I on the right lines in thinking something needs purging from the database? If so, what other table might need purging?

I'd be glad of any help as this has got me baffled

Thanks Druplers

Chris Lozinski