error at second choice while first is available?

Sorry for the title .. couldn't make at any clear.

so I'm having a problem like that :

if (versionAPI = 2) FuncY()
else FuncX()

running this on API version 2 shuts with an error

"FuncX() doesn't exist"

also tried

TRY{FuncX()}catch{FuncY()} 

and it didn't work.