How can i enable a Customer to add project.task?

The user/customer get these rigths:

                R    W   C   D
Task            x    x   x      
Partner         x   
Department      x       
Employee        x       
History of Tasks    x    x   x      
Work Order      x       
Stage of case       x       
Category of project's task, issue, ... x                
Project Issue       x    x   x
Project Phase       x    
Tasks by user and project x             
Message         x   x   x       
Message subtypes    x   x   x           
Tasks by user and project x             
Sales Teams     x       
project.issue.version   x           
project.issue.report    x

As Customer i get this error but the user have the rigth to read the partner?:

Access Denied

The requested operation cannot be completed due to security restrictions. Please contact your system administrator.

(Document type: Partner, Operation: read)