Hi, I just purchased a new VR600 modem router..everything seems to be working fine..expect one BIG annoying problem!

I have several wired and wireless clients over my network, and i MUST assign them static IP address.  Some devices you can set that on them directly, but others have to be thru the router.  I set up 9 devices already, but when i tried adding the 10th, I get grayed out as in the attached picture.  I just (sadly) read that this is a known error on some TP link routers.. is there a fix to this router's issue?  I did a check for update and it said its got the latest firmware.