Digital certificate blocked

Hi,

I'm using a macro that has a digital certificate from Thawte. Excel crashed,
and since then Excel is displaying a security warning when I start the macro
saying "this publisher has not been authenticated and therefore could not be
imitated" ... and the option to add it to the trusted publishers is unchecked
and greyed.

I uninstalled and reinstalled Office and that does not help.

Any idea of what I could do?

Thanks

MrT