This was a weird error – but I’m not the first one to see it. When using a dataview web part, and trying to do a comparison with a date column, the filter dialog wouldn’t let me choose certain comparisons. The ‘Less than’, ‘Less than or equal to’, ‘Greater than’ and ‘Greater than or equal to’ options were all unavailable, and options like ‘begins with’ were available. It’s very strange, as it’s almost like the date was a text column – except that isn’t, and that another user did get those options.
I’m not sure if this is a security related issue as the linked post seems to suggest, but it’s really weird that the two users with the same permissions looking at the same system see this field in such different ways. I don’t have a resolution, I’m afraid.