Your access privileges do not allow you to perform this action.
That's an error message that appears after you have successfully opened a FileMaker file. Thus, it appears that you can open at least one file. The error message indicates that some action taken by you or by a script is being blocked by the privilege set options for your current account.
What did you do/see just before you got this error message?
In your security settings, go to the Extended Prtivileges tab and be sure the privilege set yo uare using is set to allow access via FMNET (or I think that's what the extended privilege is called; don't have it open at the moment).