A couple things I think it could be?
Google apps install to a directory in the users profile, maybe the install location is blocked, the path to the directory on Windows 7 is C:\Users\%username%\AppData\Local\Google\Chrome\User Data\Default\Extensions.
Also we have managed Google accounts here, if a student is logged into Google Chrome using their school managed Google account we can restrict the webstore from the Google admin area - https://www.google.com/a/School_Google_Domain
If it's Google drive desktop that you are trying to install it could be a restriction on installing software (exe's).