The Upper Slabs from Chisel (Marble and Limestone) have Unnamed names, as shown on the screenshot. Ignore the Unnamed Block, report to mod author., some mod does that. And also I think these Upper Slabs should not be shown in NEI.

Sorry if this an intended feature or an already known issue.

Screenshots:

Versions:
Chisel: 2.9.2.8

If you need forge logs, modlist, or anything like that, tell me.
Thanks for the help!