Juliana --
You are seeing a known and reported bug in Project Server 2007. To work
around this bug, you will need to ask the Project Server administrator to do
the following steps:
1. Log into PWA with administrator permissions.
2. Click the Server Settings link in the Quick Launch menu.
3. Click the Manage Groups link in the Security section of the page.
4. Click the Project Managers group to edit the Group.
5. In the Categories section, select the My Organization category.
6. In the Permissions grid for the Categories section, set the "Save
Project to Project Server" permission to Allow:
7. Click the Save button.
Hope this helps.