Try changing from B/G/N to B/G only... I seem to remember someone else here saying that they had problems with their card connecting to their WRT610N when it was in B/G/N mode.
I have a WAP610N (basically the wireless access point part of the router only) and have no problems with it in B/G only mode (I've never run it in N-mode for other reasons).
My cameras: Nikon D90, Panasonic ZS7
My Eye-Fi: 8GB Pro X2