Default unable to mount system

I am having a bit of trouble swapping a new rom on my Sprint Galaxy Tab T217S as every time I swipe to flash via TWRP recovery I get the same message in the log.

unable to mount system '/

Any idea as to why that may be. My device is rooted via odin and I do have root access. Im trying to install Goodness T3 or Remedy Rom and both say the same thing.

I follow proper procedure with wiping dalvik cache, cache, system, and data also doing the factory reset.

please help this has me stomped.

thanks in advance