Sounds like your directories don't have the correct permissions. You need to CHMOD the following:
- includes/ directory: set permissions to 0777
- files within the includes/ directory: set permissions to 0666
- sessions/ directory: set permissions to 0777
- templates/compile directory: set permissions to 0777
- templates/ directory: set permissions to 0777
- cache/ directory: set permissions to 0777
- cache_builders/ directory: set permissions to 0777
- cache_builders/custom/ directory: set permissions to 0777
- files within the cache_builders/custom/ directory: set permissions to 0666
- styles/ directory: set permissions to 0777
- files within the styles/ directory: set permissions to 0666
- tmp/ directory: set permissions to 0777
- gallery/ directory: set permissions to 0777
- directories within the gallery/default directory: set permissions to 0777
To do this, use FTP software ( CuteFTP, Filezilla, etc. ) to log in to your server. On each of the directories listed above, right click on the folder and and select Properties or CHMOD if it's listed, then change the permissions as shown. If only 3 digits are allowed ignore the leading zero.
More info here:
https://www.ubbcentral.com/doc_install.php
