The most likely cause is that you may have included a character in your password which is causing an error. A common one is the £ or € symbol. Choose one of the following characters which are known to work:
! @ $ % * _ - + = ~
DO NOT use:
£ € : ? | space
...or letters with accents like umlauts, acutes etc.
Change your password by following the instructions on the IT Services site.
