On the installation guide for Webuzo it's clearly mentioned that Webuzo needs to be installed on clean server and not with a pre installed LAMP stack.
The best way to avoid the internal server error, is to upload file via FTP using the default FTP account or SSH as Webuzo user, so in this way all the files created will have the correct permission.
Edited by webuzo_manager : February 21, 2017, 6:25 am