Split the assembly into two or more parts or give the macro editor more working storage.

on z/OS or CMS, this can be done by increasing the region size for the assembler, decreasing blocking factor or block size on the assembler data sets, or a combination of both.

On z/VSE, this can be done by decreasing the value you specify on the SIZE parameter of the JCL EXEC statement, or by running the assembly in a larger partition.