HI,
those structures are from basic language,and they work if you use a basic compiler (i think in pic basic translating those to pic assembler)...perhaps you should try to rethink your program using the conditional jumps your assembler has,once again,if you are using pics,one example could be the instruction btfss (bit) ,that skips the next instruction if the bit is high....
If...Then, If A>B then..., etc Directives are not supported by all assemblers.
Your assembler must support this feature.
For example in 8051, I use ProgStudio which has this feature.
Search for assembler contain this feature.
But I'm sure it will not be free.