Update on this;
I just tried running this sql again and now I get an error message for some reason.
Why would it work fine before and not now? Nothing has been changed.
Any ideas? Thanks in advance for any help.
--------------- Added [DATE]1375561645[/DATE] at [TIME]1375561645[/TIME] ---------------
Managed to fix it for myself. It was because the fields already had the '0' data in them from the query I ran before. (silly me)
Therefore it needed a WHERE in the sql.
e.g.
UPDATE userfield SET fieldX = '100' WHERE fieldX = '0'
[hope this helps anyone else who's as silly as me]