You're giving very little information away.
I suspect you are trying to develop XSLT stylesheets using only an IE browser. This isn't a good development environment: it's fine for running stylesheets once they are working, but it's not good for debugging. I would advise developing in an environment such as Stylus Studio or XML Spy, at least while you are learning.
There's also a plug-in to IE that allows you to view the source code, but I forget where you can get it: go to the MSDN XML page and browse for add-in downloads. You can also set IE options (again I forget the details) that show you the error messages when things go wrong, rather than just giving you the ridiculous numeric error codes.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference