Outlook is a bit flaky at the best of times, and is often the culprit when memory errors occur.

It's called a 'memory leak' - you'd be forgiven for thinking this is faulty memory, but the 'leak', in simple terms, is a silly way of saying the programme doesn't use the memory properly, resulting in two programmes trying to use the same bit of memory.

Usually it's caused by a corrupt file, and an uninstall/reinstall will fix it.