The most likely reason for the NAT0376 error is using an old version of UEXIT00 with the new version of EINE.
There have been several new parameters added to UEXIT00 such as:
0260 1 +EINE-INSTALL-SITESYM-SUFFIX (A4) INIT
Verify the UEXIT00 Natural program in the EINELIB is the V18 version of UEXIT00.
Do not copy the UEXIT00 Natural program from the V17 EINELIB to the V18 EINELIB.
Use the V17 UEXIT00 as a model and update the new V18 UEXIT00 program with your specific parameter values.