Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 211)

Appendix B Micro488/EX Error Messages
B.3
18 NVRAM FAILURE
An error was detected in the NVRAM which resulted in the necessity to
reinitialize memory. Any data in the LOG and MACRO buffers is lost.
19 LOGGING ERROR
A READ LOG command was encountered within a macro.
20 TIMER IN USE
The macro incremental timer was in use when another macro with a
specified interval was involked.