cannot click on combobox and cannot insert an object

Hi guys - has anyone come across this before ? All of a sudden I simply cannot click on a combobox drop down and niether can I create a new combobox and get the msg "Cannot Insert Object".

EDIT -I have discovered that I cant insert any active x controls - and receive the Cannot insert object message

I have sent the wb to some colleagues, and others have accessed it from its location and it works fine for them!

Any ideas as to why I cant select the drop down?

Many thanks