In the QlikView Management Console (QMC) under Documents -> User Documents -> Document CALs you can assign CALs to specific users.
After assigning a user to a Document Cals and applying the change you receive an error "Too many document CALs assigned"
For more information about CALs type please refer to the following article Overview of CAL TypesEnvironment
QlikView Server (any version)
The reason for this error to occur is that you haven't assigned (enough) Document CALs to your document.
Another possible explanation of this situation is documented in this article: Too Many Document CALs allocated When There Should Be CALs Available to Use
In the same tab in the QlikView Management Console (QMC) there is parameter called "Number of CALs allocated to this Documents"
This number needs to be superior or equal to the amount of users you are assigning a Document CAL to.