http://stackoverflow.com/questions/1...aused-by-forms

I simply registered the .ocx as I said in my previous post, i.e.
Start > Run
then regsvr32 C:\Windows\SysWOW64\MSCOMCTL.OCX

This is specific to 64-bit Windows 7 (running Office in 32-bit mode, the most common scenario)
For 32-bit WIndows, the equivalent would be:
regsvr32 c:\windows\system32\mscomctl.ocx

For some inexplicable reason, the Windows updates on Wednesday night (15/08/2012) must have unregistered this file