What is causing "Automation error Unspecified error" on Worksheet_Activate?

We ran into the same problem, but with a twist - we have several people all using the same macros successfully, but one is having the "Automation Error" "Unspecified Error" problem. The other answer helped me identify that the problem might be due to the "Microsoft ProgressBar Control". (Thank you very much)

But instead of removing the form, I unregistered and registered the MSCOMCTL.OCX on the user's PC that was having problems and he's back in business again. I wish I knew what caused the registration of the control to go south - this is not the first time I've had to track down problems with this control.

To unregister and register the control:

Use an “Elevated command prompt” (command prompt run as an administrator), issue the following commands:

 Regsvr32 /u c:\windows\SysWOW64\MSCOMCTL.OCX

 Regsvr32 c:\windows\SysWOW64\MSCOMCTL.OCX

NOTE: the /u unregisters the ocx

Whenever I get strange errors like this, the first thing I do is clean the code with http://www.appspro.com/Utilities/CodeCleaner.htm. It's a free add-in, but you can do it manually too. Just copy your code out of the module and into a text file (or right click and Export). Then delete the code in the module, compile and save, and put the code back in.

When Excel compiles "on the fly" it's creating p-code which then gets compiled to machine code. Sometimes, particularly with heavy editing, the p-code gets corrupted. Copying the code out, deleting it, and copying back in forces Excel to regenerate the p-code.

I've solved some really strange behavior with this method. Hopefully it works for you too.

I found the issue. One of my forms had a control on it that apparently stopped working, and this had a ripple effect.

The control in question was "Microsoft ProgressBar Control, version 6.0". I do not know WHY it stopped working, but removing the form (and, of course, all references to it) resolved the issue.