Error when deleting a task from a quote (when creating a quote)

Please find the steps I follow when adding and removing a task within the process of creating a quote.

  1. Added a completed task as a line item.
  2. Saved the quote.
  3. Then again I tried to remove the task (line item) from the quote.
  4. System show a red icon after clicking the delete button, showing that the line item is removed.
  5. Save the quote once again
  6. System show a red popup after few seconds delay.

Please help me on the above issue. Is it not possible to remove a line item from the quote after saving it. Mainly for tasks?