TS01 error in sale

Hi Experts,

Im creating a contract Through TS01 for mutual fund (Type - 02A). However I dont have any quantity of mutual fund or any opening balance , still system is allowing me to sale the security.

Warring message given by system is

Messages relating to transaction

Per 17.12.2011 a negative balance of 5000000.000000- Units exists

Short position in accounting code GNPL, val. area 001, ID No. 69, date 17.12.2011

I want to know how can I convert this warning message into error message..?

Regards

Ashwini