While installing Windchill 11.1 M020 CPS05 earlier today, I received an error in the logs, telling me that the install had failed because the file name or extension was too long. After the failed install I am unable to start the methodserver.
The PSI allowed me to install Windchill 11.1 M020 with the longer path (base path was c:\PTC\Windchill11.1_Application) and completed successfully. It was only when I attempted to install a new module (ERP connector) that this problem surfaced.
It appears that Java cannot parse a particular path in an XML file during the install, due to it exceeding a maximum length.
My suggestion, therefore, would be to have a warning or a check in the PSI, when installing windchill, to prevent the path length from exceeding a certain value.