Can't synchronize :(

Hi all,

I've been having trouble with DW recently, first the Commands menu broke down
twice, and now I can't synchronize. When I try to, I get the following message
: "While executing SiteOptionsSiteMenu_Synchronize command in menus.xml, the
following JavaScript error(s) occurred: Exception thrown in native function"...

What does that mean, and why is this happening? I uninstalled and reinstalled
DW twice in the last two days, hoping this would get rid of my problems, but it
obviously hasn't.

Anyone got a clue?

Thanks,

Rob