Typically NX uses the folder specified by the ENV variable "TMP" (not "TEMP") (or the "Start in" folder) for the temporary file folder.
In NX, do a File -> Help -> Log File
Search for "ugii_tmp_dir"
compare to the OS level env variable "TMP"
Do you have write access to this folder?
Note it could be changed in an env.dat file (see if UGII_ENV_FILE is set by searching the log file)
and/or the "Start in" folder could be set differently based on the "start" shortcut used to start NX and/or a .BAT file used to start NX.
The next time this happens, if you look in the log file, it may display more info about what specific folder it is having problems with.
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled