On Firefox have you made sure that the Silverlight plugin has been activated, via Tools > Add-ons > Plugins - set it to "always activate" if it is set to anything else.
For the error has occured error try this:
Open up your clock down in the right hand corner.
Click 'Change date and time'
Click 'Change calendar settings'
Under the 'Date' tab, make sure your date formats are the same, ie. dd-MMM-yy
for short, dddd-MMMM-yyyy for long.
Make sure the time zone is set to the UK.
Make sure the date are set to UK (English) and not UK (American)