Well yes, hex is written in upper case. But this is a GUID, which is frequently stored as a text string, and is case-sensitive. Google for upper/lower case GUID and you'll find all sorts of pain; some systems generate GUIDs in upper case, some in lower. For those database systems that have a field type of GUID, most will return their text form as upper case, but not necessarily all do. If in any doubt where your GUIDs are coming from (e.g. a URL querystring) always be aware when doing comparisons! :-)
Telegraph marker posts ... nothing to do with IT Phasmid email discussion group ... also nothing to do with IT Beekeeping and honey site ... still nothing to do with IT