Cannot delete relationship that has been created initially.

Krishan,

there is no specific option or setting to permanently or "not-permanently" un-link activities in P6 or whatever; you should be able to delete the relationship between two specific activities either by double-clicking the relationship line and display the small dialog box where you will click "Delete"; or display the Relationships / Links tab in the Task Detail form, select the task you want to unlink, select the Predecessor or Successor side, select the link you want to supress, click Supress

however, it happened once when I was giving a trainin session that one trainee was not able to unlink tasks at all; the only way-round I had found was to delete the tasks and create them anew; I guess there is a bug somewhere in the software, that creates this behaviour

Hope it helps

Alexandre