Maximal size for a compiled program

[RandomiserUsr]

Learn how to use RAM banks in ZX Spectrum 128k. Then compile data blocks as different taps and make a loader. I'm using ZXBlockEditor for gluing blocks in one tap. But now I use assembler.

I am having issues on the RAM banks.  I try to use bank 4 but when I switch it to 4 the program crashes.

Code:

sub FASTCALL setmemorypage4()
ASM
 LD      A,(0x5b5c)     
 AND    0xf8
 OR      4              ; Bank 4
 LD      BC,0x7ffd
 DI
 LD      (0x5b5c),A
 OUT    (C),A
 EI
END ASM
end sub

I have another one for setmemorypage0() which I call after working on page 4 but never gets to that point.
I do think its a mem clash but hard to track down.

thanks