1> jz 0x12345678
1>error: invalid use of symbol.

You forgot to provide the context - I suspect this an object output format, or relocatable PE, because 1.69.37 has fixed a bug in relocatable formats that allowed earlier versions to assemble jumps to absolute addresses even though it was not able to generate appropriate relocation for them (and thus it was generating incorrect code).

Tomasz Grysztar
But the error message does not look very informative. I also got that message in an MS COFF which was perfectly compiled by 1.69.35 (and also properly worked), but not with 1.69.37. That was actually my bug, but I spent hours to understand, what this error message is supposed to mean.

I reused the same error message that is signalized in analogous situations when you use some relocatable symbol as target, without much thinking about it. I often just re-use existing error messages for all kind of even slightly-related errors, my fault.

Known issue: http://board.flatassembler.net/topic.php?p=134817#134817 FAQ B 3

http://board.flatassembler.net/topic.php?p=137175#137175

DOS386
That's not the same. FAQ B3 shows a situation, where one possible error message is chosen to be displayed in an ambiguous context: one tries to use a non-base register either as a symbol or as a base register. However in most cases a newbie knows, that cx is a register, but does not know it can't be a base register.

Regarding the subject of this topic an error message like "the address expression is not applicable in current addressing context" would be (as it seems to me) in any case a better option.

Well in fact FASM stops at the wrong line. It's just one line and you can think what could be false. This would not be much characters in most cases. I even use some general error messages which seem to be the nearest error case. In the case above it would be the best to tell that "cx can not be used as base register". So with the name of the register itself.

In my eyes the deepness of the error messages in FASM are okay. Not perfect but where can you find perfect software excepting your own programming kitchen.