Error on page

Some of my machines (mainly developer machines) have stopped displaying .net
user controls on an ASP.Net web page. Other machines in the office are fine,
I am fairly certain it's not a server side issue as it the issue seemed to
correspond with people downloading updates.

The web page displays the X and the error in the toolbar, say object doesn't
support this method or property. The server app hasn't changed. Any help
would be appriciated.