Another qkview is running. You can't run multiple instances of qkview at once.

Hi

When trying to generate a qkview file from the GUI nothing is happening. When trying to do it from the command line I get the message "Another qkview is running. You can't run multiple instances of qkview at once." Can anyone advise?

I am a complete novice with these devices so apologies for my ignorance as I am only just starting to learn.

Many thanks in advance.