Predecessor Relationships Constraint not working in Plan activites(ProjectLink)

I am using Windchill ProjectLink 10.2 M030.

I have created a project plan which has 5-6 activities, which needs to start after one another.

i.e Activity 2 must start on completion of Activity 1 only and Activity 3 to start after completion of activity 2 and so on.

Hence in activty 2, I have given the predecessor relationship as "1FS" and in activity 3, "2FS" and so on.

But on starting the project, all activities are available at the same time for respective users and activities are not following the reqd sequnce.

Activity does not wait for predecessor avtivity to complete.

Has anyone faced similar issues while working on ProjectLink? Any help regarding the same would be appreciated.

Best regards

Sharath