QlikView works with a in-memory data model.
So, when you open the application all the data will be allocated in the computer RAM memory.
Depending on how much memory you have available (considering that you may be running other programs on the machine) and on the data you are loading or analysing, when there is no memory available you get this error.
I suggest you check how much memory you have on your system when you open QlikView using windows task manager.
Hope this helps,