"Import -> Schema Settings" Checkbox Functionality

I am trying to import activities from one course to another. When I get to the "Import -> Schema Settings" page, where I should be selecting via checkbox the actual activities I import, I find that one of two things happen:

1. I am able to check/uncheck any given box, but there is a lag of up to ten to fifteen seconds between the time I check the box and the time the check appears in the box.
2. I am unable to check any box.

The "Check all/Uncheck all" link works in both scenarios, but it always works with the same kind of lag described in scenario one above.

I am unable therefore to import selected activities. Any suggestions?