ScribusPortable - lost SLA association

My computer lost the .sla file association to ScribusPortable (and many others as well, due to a power cut - I've been able to get others working). Any idea how to get it "restored" i.e. that by double clicking an .sla file it would be opened in a ScribusPortable?

Now it opens an "Open with" window and asks to choose the program I want to use to open the file. If I click "Browse" and browse to the hard drive folder where the ScribusPortable.exe is and choose it, it doesn't show up in the "Open with" window. The same happens if trying to change the SLA file associated program via Associate a file type or protocol with a specific program.

What can I do?