errors in mysql syntax

ALTER TABLE TimeTracker.TT_ProjectMembers ADD
        CONSTRAINT FK_Roles_Projects FOREIGN KEY
        (
                ProjectID
        ) REFERENCES TimeTracker.TT_Projects (
                ProjectID
        ) ON DELETE CASCADE ,
        CONSTRAINT FK_WorksOn_Users FOREIGN KEY
        (
                UserID
        ) REFERENCES TimeTracker.TT_Users (
                UserID
        )



As iam new to this mysql when i was doing the program mysql shows the error as

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'CONSTRAINT FK_WorksOn_Users FOREIGN KEY
        (
                UserID
        ) REFERENCES TimeTracke' at line 8


what to do if this error comes plz anyone help me