Have you opened any other qlikview documents created by another qlikview installation, for example documents you downloaded from a site like this one? Each time you open a document created by another user the license code of your Qlikview Personal installation will change and you can't open documents created earlier anymore. Your license key has now changed four times and you can only create new documents and open these new documents. Anything created before or by others can't be opened anymore.
You should be able to open files created with your user in the same computer any number of times. But if the file was created in the same computer with a different user, or in a different computer you won't be able to open it. You can find more details about it in the following article:
The simple solution: buy a standalone user license.
The complicated solution: create a virtual machine in a tool like vmware workstation or VirtualBox and install Qlikview in that virtual machine. Make a backup copy of the virtual machine (or a snapshot). Each time you need to check out a sample document start up the virtual machine and check out the sample in the virtual machine. Use a copy of the virtual machine each time and discard it afterwards.
I've seen prices of 1.010 € per local client license. But I'm not sure if that price is still actual. You'd have to ask a Qlik Partner or Qlik Sales representative. And don't let them tell you that you can only buy Qlikview Server SMB with a minimum of 5 user cals. Single local client licenses are available if you insist a bit.
