You might be able to tweak *control
Change:
8020 LET mx_ln=MXL(0)+1,mx_cl=MXC(0)+1
To:
8020 LET mx_ln=MAX(25,MXL(0)+1),mx_cl=MAX(80,MXC(0)+1)
This should allow it to avoid the error 29.
(BTW: The password for *control is "password" so as to avoid trace output)