problem in inforecord

Hi Experts,

I have a Problem While Creating Purchasing Info Record. After Entering the Default Values such as Planned Delivary time,Standard Qty,and Net Price,Once i press enter it Says " Make an Entry in all required fields" .I came to know that the mandatory field " Valid To" is greyed out. I tried various method but its the Same screen the " valid to" option is greyed out i can't enter the date and without entering the date i will not allow me to create info record. What shall i do please help?.

Regards

Anubhav