PRIMARY LOAD CASE CAN ONLY BE ADDED IF SET NL COMMAND IS USED.

The SET NL command is used in a multiple analysis run if the user wants to add more primary load cases after one analysis has been performed. Specifically, for those examples, which use the CHANGE command, if the user wants to add more primary load cases, the NL value should be set to the maximum number with the SET NL command. The program will then be able to set aside additional memory space for information to be added later.

For example, if you specify 50 primary load cases prior to Perform Analysis command and later you include another 50 primary load cases after the CHANGE command, you need to specify SET NL 100 (or more) command so that program allocates the extra space in memory to include additional number of load cases.

Thanks Suro It was helpful