The user doesn't have the proper system resources to enable EZTalk to display information correctly. The solutions to 1 and 2 are simple. Unregistered users need to register if they wish to reserve a nickname. And logging off, changing their user settings and logging back on using the correct password will solve number 2. Assuming they are using the wrong case in the password or whatever the problem is.
System resources are another issue entirely.
There are many variables here. Especially when dealing with older systems. But our QA department feels strongly that a lack of system resources is the cause for many of these complaints. Especially if this is an intermittent problem. That is, make sure you are really registered, and that you are entering your password correctly.