Unable to set Installed property of Add in class-Excel error Citrix

Hi
I have access to this application on citrix server via their website.The application launches an excel utility and only that application has that vb code where all add ins are getting installed.It is working fine for all users till now.

Recently two users started getting this error "Unable to set Installed property of Add in class" when they try to access that application.

Please help out because we have tried everything from deletiing all sessions and all but can't get to any conclusion.The user can access the utility fine in below environments like dev and QC but the problem occurs in PROD.

Thanks in advance.