Ribbon/COM Class not registered error

[bpie...@gmail.com]

I have a single user that started seeing an error dialog showing a "Class not registered" error when starting Excel. This started happening on a single machine after a security update, though I'm not sure what else could have been updated. Other machines that were updated do not see the issue. Nothing was listed as "disabled" in Excel.

The IT guys tried all of the various steps found in similar issues here and online, including clearing registry entries, re-installing Excel, etc to no avail. Based on my search of this group and online, I strongly suspect this is some corruption on the Excel/Office/Windows install, but throwing this out in case anybody here has seen this and is aware of a possible specific cause.

The add-in still works fine for the user, so to avoid the error popping up when Excel is opened I just gave him a version that does not try to interact with the ribbon menu.

Here is the specific error shown. Thanks in advance if anybody has any ideas:

ComAddIn [Error] The Ribbon/COM add-in helper required by add-in <...> could not be registered.
This may be due to the helper add-in being disabled by Excel.
To repair, open Disabled items in the Options->Add-Ins page and re-enable target add-in, then restart Excel.
Error details: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Runtime.InteropServices.COMException: Class not registered
--- End of inner exception stack trace ---
at System.RuntimeType.InvokeDispMethod(String name, BindingFlags invokeAttr, Object target, Object[] args, Boolean[] byrefModifiers, Int32 culture, String[] namedParameters)
at System.RuntimeType.InvokeMember(String name, BindingFlags bindingFlags, Binder binder, Object target, Object[] providedArgs, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParams)
at ExcelDna.Integration.ExcelComAddInHelper.LoadComAddIn(ExcelComAddIn addIn) : TargetInvocationException - Exception has been thrown by the target of an invocation.

Brian