Zoho Creator Blues

Is anybody else having problems sharing apps in Zoho Creator? About a week ago I started getting calls from Users with whom I had shared apps. They were logging in as usual but getting an error message:
You have logged in as (xyzabc). You are not allowed to access this view.

When I checked the apps it showed they were still listed as shared users. I had not exceeded my user quota. My own login (as Admin) was working fine.

Despite all that, when I tried to log in as them, I got the same error message. In some cases these are users who have been using the system for years without problems.

Sometimes if I delete the User and then Share he app again, it will work fine for a while. But then the same problem recurs.

I have contacted Zoho support six or seven times now but don't seem to be getting anywhere. They haven't even answered the last few messages.

ANYONE GOT ANY TIPS??!!

It may be a clue that when I look at my list of shared users (ie by marking an app to share and then clicking on SELECT USER) I see a list that has both ID names and email addresses. ie there appear to be two different formats in the way users are listed. When I add them afresh just the ID name appears in the list of users the app is shared with. At this point I can log in as them and it works. BUT sometime later the email address will appear in the list of shared users instead. When this happens I invariably find that the user no longer has access.