I think I realize the error. Val(%logonserver%) will not work due to the "\\" at the beginning. Try using this instead when you need to get the server number...

 Code:
$servernumber = Val(Split(%logonserver%,"\\")[1])
$server = "\\"+$servernumber+"FNP01"

You can then use the new $server variable further down to map your drives.
For example...
 Code:
Use i: $server+"\sharename"