I have the same exact problem. I checked the paths and the needed folders are there, with 755 permissions.
Warning: move_uploaded_file(/var/tmp/phpyz3hIF) [function.move-uploaded-file]: failed to open stream: No such file or directory in /home1/CLIENT/public_html/libraries/joomla/filesystem/file.php on line 351
Warning: move_uploaded_file() [function.move-uploaded-file]: Unable to move '/var/tmp/phpyz3hIF' to '/home1/CLIENT/public_html/tmp/Mobile-Joomla-0.9.10.zip' in /home1/CLIENT/public_html/libraries/joomla/filesystem/file.php on line 351
These folders exist with 755 permissions:
/home1/CLIENT/public_html/libraries/joomla/filesystem/
/home1/CLIENT/public_html/tmp/
I have RSFirewall installed.
I just uninstalled RSFirewall and the installation was fine. FYI! I'll let the RSFirewall developers know.
thanks,
Hope