The way you've written that is somewhat ambiguous - you appear to state that the seat map was available to you to choose your seat after the seat change initiated by Air France (how did you find out that had occurred?). So why didn't you choose a seat then? Or did you, and you just don't see the seat map anymore and may still have your chosen seat assignment?

With so little detail, it's probably best to start with the basics.

A) if you leave it for a while, and come back on a different day, can you load the seat map?
B) have you tried using a different / newer browser, or from a different computer?
C) have you tried accessing the booking via klm.com?