Wow talk about coincidence, I too have exactly this problem and my name is also Chris K, I guess ISPConfig doesn't get along well with us :P
Anyway, I'm compiling this for ARM. I have no idea if this problem is related to that? I would have assumed that because it's compiling Apache/PHP and not using a binary it would be OK but I guess it could be the case the scripts don't detect ARM?
This thing took around 5 hours to compile, is there no way of running this from my exisiting LAMP setup? I'd prefer that over running two servers.
If not is there any software similar to ISPConfig? I'd really like to use ISPConfig, it looks great but going through the painfull 5 hour process to recieve another fail message isn't something I want to do :S