Finally I got this issue resolved !! I don't have a rational explanation for this, all I did was to insert a SD card in the SD card slot of the camera and it just started working. I was able to take exposure greater than 30s. If anyone has some explanation for this I would like to hear it - for some unknown reason, the shutter trigger for longer exposure is tied to SD card being present in SD card slot????
Thanks all for pitching in, really appreciate it!