I have an SQAi and after not being used for a while it would not fire even though the battery check light lit.

What sorted it for me was cleaning the battery terminals in the camera base. I rubbed all the pins with some fine wet and dry paper and dusted clean and all has been good since. Not sure if the SQB uses the same 4 button type batteries ?

If it does may be worth a try.

I think I have read on the net somewhere also about films backs not being synced with the body properly causing lock ups, may be worth a search.