To All the Gurus who have provided valuable advice:

HATS OFF TO ALL OF U AND THANX A LOT
I am OVERWHELMED at the response.

I wanted to check the impact of change in every parameter so
I did the following in the order specified
Increase large_pool_size to 300 M (Error Kept Coming)
Decrease sort_area_size to 150 M
Decrease sort_area_retained_size to 75 M (Sorts remained in memory)
Increase Shared_Pool size to 500 M

Haven't got the problem since 21st March and hope it stays
away. I am now setting up statspack to get in on the various
ratios and figures.

I also am of the view that sort_area_size can be reduced furthur
as 100 % sorts are taking place in memory.

I believe statspack reports will help me in arriving at better values
yet.

Thanx a lot again

Best Regards,

Kashif