Can't install 1.5.1, incorrect PHP version reported

Hello there,
I’m trying to upgrade from 1.4.~ to 1.5.1 but it fails at the requisites screen reporting PHP version inferior to 5.6, but as you can see in my screenshot PHP actual version is > 5.6. Any hint about this issue?
Thanks in advance, Alejandro.

Forget it, with phpversion() it shows 5.5… I don’t know about that PHP version.
Thanks anyway.