Hi Ryan,
Thank you again for your kind reply.
Sorry, it didn't work by disabling timingandestimationplugin.
I have worked out what the issue is. I have created a fresh trac.ini by initenv and with this when I restarted the trac it gave dropdown box Milestone: in the Create-Ticket form. Then I started to look for the offending configuration parameter which causes Milestone: disapprearing from the Create/Modify form. Finally, after carefully adding each section to the new trac.ini I found that it was the following configuration which was causing the issue:
This was the earlier configuration which caused Milestone: dropdown disappearing from the Create/Modify form.
[trac]
permission_policies = DefaultPermissionPolicy,LegacyAttachmentPolicy
And when I added DefaultTicketPolicy to the above line then Milestone: dropdown started to appear again in the Create/Modify form
[trac]
permission_policies = DefaultTicketPolicy,DefaultPermissionPolicy,LegacyAttachmentPolicy
Thanks againg for the help.
Regards,
Iqbal