Indian Railway Catering & Tourism Corporation [IRCTC] — Tatkal ticket not getting booked when available. Premium tatkal ticket is getting booked.

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Website:	www.irctc.co.in/eticketing/loginHome.jsf

I was booking an online tatkal ticket(on IRCTC) for a journey from Secunderabad to New Delhi. I entered all the details on IRCTC portal. Also, the tickets were showing available. But after entering all details and clicking on Pay button at the last moment, it(IRCTC) did not book my ticket.
I thought there was some technical error, I tried again, and it was still showing Tatkal tickets available. I filled all details and then atlast, same happened as before. Now, I tried for Premium Tatkal booking. I had to book the ticket because of emergency, I agreed to pay more than double the amount of ticket(premium tatkal ticket is dynamic and fare of ticket increases). And this time in first attempt the ticket was booked. it means that there is some issue with the IRCTC Tatkal ticket booking.
The ticket fare of premium Tatkal increases with respect to demand, that is, the number of people booking the ticket. So, with the above IRCTC Tatkal booking issue, we can estimate that the IRCTC is not simply allowing the Tatkal Tickets to be booked so that more and more people go for premium tatkal and fare of that increase and IRCTC make more money. I really believe, It is also something like IRCTC is booking Railway tickets in Black then.
Its really impossible to book a Tatkal Ticket on IRCTC. It happened not once but two times.
Second time it happened when I was booking a ticket for a return jouney(New Delhi to secunderabad). and this time too, same issue occurred.
This is my grievance. Hope, i get justice...Please contact for any information on tickets that i was booking.