This is because the Training Log needs a lot of memory (big scroll pane). The problem is that this memory need to be in one piece (bitmap), and therefore the problem may occur even if there's still a lot of free memory.
We'll soon provide a new release that needs less memory.
Today I wanted to add one manual training, but application closed with message "out of memory". This is strange, becuase there was 31.8MB of free RAM (with app running).
Here you can see capture of this (bit low on quality):
http://pumori.pl/rungps_outofmem.wmv