Adobe Reader PlugIn. "Class Not Registered"

I have written a simple PlugIn to liase with out Document MAnagement software, all the system does is essentially log the current open file and pass that to an external DLL call for the document manager).  This worked find but as of a month ago when trying to initialize the External DLL is claims Class Not Registered (from the compiled Add-In, that was working the previous day.). 

I have now taken all the external dependancies out of this DLL so all it does is display a message box, same thing.  I have compiled both the plugin and external DLL in 64 bit and 32 bit and still the same (using the appropriate regasm tool to register it).  This isn't just on a local machine though,,, it occurs on all I tested on,

Have come to a bit of an impasse and need help or guidance.

Thanks in advance

Danny