Using a PHP setup on a Windows 2008 server as per the FastCGI instruction set I found that installing Sugar 5.5 stopped at the SystemCheck page (install/installSystemCheck.php) with a message that the message

The session.save_path setting in your php configuration file (php.ini) is not set or is set to a folder which did not exist. You might need to set the save_path setting in php.ini or verify that the folder sets in save_path exist.

The general comments on searching for ideas were that the is_dir function fails regardless of the existence or otherwise of the directory.

I delved a bit deeper and confirmed that the is_dir function is restricted by the openbase_dir setting and if the session.save_path is outside the openbase_dir setting then it is not found.

I also noted that the php chdir function is limited to the openbase_dir setting.

Using multiple values in the openbase_dir setting does not work either as apparently is_dir ignores the secondary setting.

In any case the only way around this is appears to be to have the session.save_path within the openbase_dir path.