I am having the same issue but on a different platform. I am running Ubuntu Server 14.04.1 Apache with php version 5.5.9. I have checked for the proper permissions and they should be correct. The user/owner of the files is the same as the user is the same user as apache. (www-data:www-data) I have gone as far as granting full read, write, execute for all users which I don't like to do because of possible security issues.
Here is the log entries for when I try to install an extension/theme:
[25-Sep-2014 18:32:50 Europe/Berlin] 0:WhitewaterDave:archive.inc:381: is_dir() expects parameter 1 to be a valid path, string given
[25-Sep-2014 18:32:50 Europe/Berlin] 0:WhitewaterDave:archive.inc:382: mkdir() expects parameter 1 to be a valid path, string given
[25-Sep-2014 18:32:50 Europe/Berlin] 0:WhitewaterDave:archive.inc:411: touch() expects parameter 1 to be a valid path, string given
[25-Sep-2014 18:32:50 Europe/Berlin] 0:WhitewaterDave:archive.inc:395: fopen() expects parameter 1 to be a valid path, string given
[25-Sep-2014 18:32:50 Europe/Berlin] 0:WhitewaterDave:packages.inc:165: gzopen(../modules/_cache/zen_import-2.3.15-1/_init/config): failed to open stream: No such file or directory
[25-Sep-2014 18:32:50 Europe/Berlin] 0:WhitewaterDave:archive.inc:462: gzopen(../modules/_cache/zen_import-2.3.15-1/_data): failed to open stream: No such file or directory
I get the same errors when I try to install zen import and PayPal import, as well as a couple of themes.
I read that it is possible to install the extensions manually but I haven't come across the instruction for doing that, at leas none that worked. Your help will be greatly appreciated.