I can open a document once, but the whole computer locks up on the splash screen when I attempt to open it again – 64 bit computer running 32 bit Vista

This issue is caused by the Windows sidebar being open.

Close the Windows sidebar, prevent it loading at start-up, reboot the computer, and the document should now open fine.

Alternatively, upgrade the viewer software to version 2.5.82 or above as this fixes the issue.