Update September 15, 2015: Recently Bangladesh Parliament has amended the Foreign Exchange Regulations Act 1947. The requirement of and 18A and 18B Approval from Bangladesh Bank has been removed.
You can read about the amendment here.
Bangladesh Bank on 10 March 2015, through FEID Circular no. 01/2015 provides a new list of required documents. In the circular, Bangladesh Bank also informed that all application must be made through online, no hard copy will be allowed from now on.
If you are a foreign investor, or run a Liaison Office, Branch Office, or have a buying house, you should take a look at the Circular.
The circular is in Bangla. You can download the circular from here.