hmm, looks like the version is ok.
I don't see why it fails, but you could just disable the php version check for now.
in ubbthreads.php find:
if(!version_compare(phpversion(), "4.3.0", ">=")) {
print "<b>Fatal Error:</b> UBB requires PHP 4.3.0 or higher. Your PHP version: ";
print phpversion();
exit;
}
Just remove this section to disable the check.