The newest version of Excel Add-in, 11.0.1.15, from HP's Live Network site, list the following workaround for the error.  They state that this can occur for an install without admin privileges, but I have seen this error occur when an admin was logged on a workstation and ran the install.  But the fix was used as suggested and corrected the issue from occurring.  
Error: ''Compile error in hidden module: mdlGlobal''
From the new readme for 11.0.1.15:
Error when Opening Excel: If you installed the HP ALM Microsoft Excel Add-in without administrator privileges, you may receive the ''Compile Error in hidden module: mdlGlobal'' error when you open Excel. The Windows Common Controls mscomctl.ocx file has become un-registered. To resolve this issue, either:
 - 	Repair or reinstall Microsoft Office. By default the mscomctl.ocx file is registered when Microsoft Office is installed.
 - 	Manually register the mscomctl.ocx file:
 - 	For 64bit OS, run the following command in the cmd window with administrator privileges:
Regsvr32 c:windowssyswow64mscomctl.ocx
 - For 32bit OS, run the following
   command in the cmd window with
   administrator privileges: Regsvr32
   c:windowssystem32mscomctl.ocx**