Microsoft CRM 4.0 ASP.NET Error 1309 - CRMException - maximum user quota

I was working on a Microsoft CRM 4.0 system the other day for one of my clients. It's mainly used for demo and testing purposes so it hadn't been used in a while.  The customer was unable to login to the server.  When they tried to login to CRM via the browser, they just got a message saying "Invalid User Authentication".

I spent quite a while checking security settings, IIS settings, etc.  Didn't really see anything CRM-related in the server event logs either. But I did see one error showing up at the exact moment the user was trying to login. But the source wasn't MSCRM, it was ASP.NET 2.0.50727.0.   Event ID 1309.

There was a long list of details on the error but the part that jumped out at me said this..
Exception type : CRMException
Exception message : You have reached the maximum number of user quota

So it sounded like they had more active user accounts than licenses. This is possible since the company was imported from another domain with different user accounts and probably not mapped appropriately. I think originally they were on a 30 trial installation and hadn't registered it so maybe that gave them an unlimited number of users during the trial period?  Since I had just registered it earlier to solve a different error, that might have kicked in the quota problem.  Though it seems like the browser login should have told them about being over quota, rather than having to dig into the server logs?

Anyway, I ended up going directly into the SQL tables and making some changes. I went into the SystemUserBase table. I was looking at the IsDisabled (bool) column.  Should be "True" for disabled users.  After counting the number of active users in the table, they were definitely over their 5 user license.  So I manually changed the IsDisabled value to "true" for all but 5 users.   Then I was able to login to CRM with no errors since they were now within their quota!

While you are there, you can also adjust the TYPE of user account via the AccessMode (int) field. 0 for full access, 1 for administrative access, 2 for read-only access. But this isn't necessary to fix the user quota error message.

I didn't see this error documented anywhere else so hopefully this post will show up in Google and help some other folks.