Tool tips & date field not working on join form

For some reason a couple of things have stopped working on our join form:

When you hover over the info icons the little question mark pops up next to the cursor, but the tool tip / caption isn't displayed. (This is the same for all fields). Also, if you click into the date of birth field it no longer displays the calendar pop-up.

The strange thing is that both of these things work OK on the edit profile page. 

Has anyone any ideas what might be causing this?

It working on the edit page and not the join page is a good thing.  That means something on the join page is interfering with the javascript that is not on the edit page.  Turn off js cache and compression if they are on so you can examine the pages.  Look for what is different between those pages.

Spot on Geek Girl - it was a problem with the JS cache, I cleared the cache and now it works fine. Thank you!