There have been errors found in MASM while using the previous version of this macro. Those errors are hard to debug and you should discontinue use of that macro. Luckily, a solution was found by Maelstrom and implemented looks like:
I have posted this here because there are several threads here because of this problem and maybe some people don't read all the threads. If you use many macros then you should read the thread outlining the class of errors created by MASM.
CTEXT MACRO y:VARARG
LOCAL sym, [b]dummy[/b]
[b] dummy EQU $ ;; MASM error fix[/b]
sym db 0
sym db y,0
EXITM <OFFSET sym>