Environment variables will look like below in environment where shared drives are used for the user profiles,
HOMESHARE=\\<server name>\<share name>
Installations fails if there is UNC reference in the PATH environment variable, Changing the above environment variables doesn't not help, windows will revert back , only way to modify these are changing the group polices or changing the user terminal services in the Active directory.
But most of the cases you mayn't have access to group polices or AD to change the user profiles related in corporate networks.
I tried to install portal (WAS) had the same issue and tried to follow the options specified in the below IBM support article but that doesn't help me
Finally had to disable all network drives for the successful installation of Portal (WAS).