Check TP website 3G compatibility list...

Is it a discontinued one ? Can not even find it on their website!!! Only TD-8810 without B.

not clear...

Seems there is something wrong with the Range Extender.... Is the wireless channel of your router solid ? Is there any IP conflict among your computer and the extender and the root router ?

http://www.tp-link.com/en/support/3g-comp-list/?model=TL-MR3220&location=1963 Heard no such a plan.........

Should be OK.