Routine "Invalid class string"

Good morning!
I’m starting to get a bit agitated with EndNote X5: the “Invalid class string” error has begun to return on a routine basis.

Windows 7 laptop - UAC: “Notify me only when programs try to make changes to my comp”, EndNote X5, Word 2010 - EndNote/Acrobat Add-Ins, macros enabled (only font-changing macros)

About two weeks ago this error happened again, so I successfully followed this procedure:
1) Run EndNote.exe as Admin
2) Regedit → EndNote15.AddinServer (double click)
3)  Deny full control to Everyone, then re-Allow full control to Everyone gp.
4) Close everything & reopen Word 2010 (normally - no “Run as Admin” for anything - also avoids “Elevation” error 

Primarily one EndNote file that used to be with X4 - links to 5+ Word documents,  
the Word docs routinely go to people who may be using a similar biblio with X4 or 3 or 2 or 1…,
regedit still has record of X3/X4 in it, but Word Add-Ins (& Ribbon Tab) show X5 for any C:/Program Files…/EndNote/15/… though Cwyw.dotm in /AppData/ doesn’t tell me if it was X3/X4/X5 in its address

Could somebody please tell me why this is happening and how to resolve this issue permanently??  It doesn’t matter what version is going around the office from X1 to X5 on my home comp, I am always plagued at some point in time with this error!

Thanks in advance,

A recent update was issued for X5 (Windows) which upgrades the program to X5.0.1 -

Are you running X5 with or without the update?