When all maps are loaded, PS takes up between 700 and 960 MB of RAM, depending on which map you actually are in. Therefore, 512 MB of RAM will make for a lot of swapping with either load all maps or keep maps loaded, because windows itself also eats up 100 - 200 MB.
What may have happened, though, is that you ran out of harddisk space so that windows couldn\'t allocate more VM. In this case, the possible culprit maybe psclient.txt, which grew insanely large before the recent update. Deleting it will free up diskspace and enable you to upload dumps.