Original Masm32 code:
.WHILE TRUE
INVOKE GetMessage, ADDR msg,NULL,0,0
.BREAK .IF (!eax)
INVOKE TranslateMessage, ADDR msg
INVOKE DispatchMessage, ADDR msg
.ENDW

FASM code:
.while TRUE <--------ERROR (Why?)
invoke GetMessage,Msg,NULL,0,0
or eax,eax
je .exit
invoke TranslateMessage,Msg
invoke DispatchMessage,Msg
.endw
.exit:
Why does not work?
Please, give me examples!!!!

Remove TRUE, the .endw will generate a jump to "invoke GetMessage" giving you an infinite while loop

Fasm .while is a macro that resolved to testing the argument using asm instruction (i.e cmp).. thats why u cannot use constant as argument.

Partially true, if you put a constant on the right it compiles. For example ".while eax=0" works but ".while 0=eax" not (at least in Fasm 6.2 package)

i mean a constant by itself.

I updated the IF.INC to do well also in such case -please try with the latest fasm for Windows package.