Your question have 2 configuration problem.
- File Permission (in Filesystem)
- ErrorDocument Attribute (in Apache Webserver)
First, You can solve permission error using 'chmod' and 'chown' command.
try this:
- chmod -R 777 directory (777 means allow permission for all)
- chown -R [user]:[group] directory (generally, the same [user] and [group])
Second, ErrorDocument handle error can occured from invaild ErrorDocument attribute setting in .htacess or httpd.conf(or apache2.conf) file.
try this:
- check your .htacess file in 'install/' directory. If you can not check this file, you can try 'ls -al' command in terminal. you have to find 'ErrorDocument' attribute, and remove or correct it.
- check your apache webserver configuration file (httpd.conf or apache2.conf). If you can check 'ErrorDocument' attribute, you can try remove this attribute in file. It is temporary, so you must backup it before try suggested cases.
- If you can not solve by case 1 and 2, you can try disable 'AllowOverride' attribute. Try find 'AllowOverride x' attribute and replace to 'AllowOverride None'. Because, this problem can have possiblity from .htacess file in parent directories. AllowOverride attribute can control allow or deny additional configuration in .htacess file.
- You must restart apache service after try this cases. you can try 'service httpd restart' or 'service apache2 restart' command.
Good luck to your web server and you.