error message

Does anyone know what to do about this error message in DW MX2004 while
defining a site?

I have Windows XP Professional.

The error While executing DWMenu_Site_DefineSites command in menus.xml, the
following JavaScript error(s) occurred:

Exception thrown in native function.

I started having this problem today with Dreamweaver MX 2004 in Windows 2000.

I could only open the site that I was on when the trouble started. I tried
rebuilding the cache for that site but got a fatal error too (didn't write it
down).

I then tried deleting all the other sites and creating a new one and that
didn't work. Finally, I tried deleting the sole site left. When I did, it
rebuilt the cache (after a short time when there were 2 of the same site listed
and I deleted one of them).

Bottom line was that, after I rebuilt that site, I could add other sites back
in.