Unable to change lot on-hand date

Hi,

I have a lot which is having effective date less than the on hand date. For example Effective date: 12/15/2016,  On hand date : 12/15/2020.

I am not how sure how this was happened.

I need to change the effective date to 12/31/2016 then system throwing hard error that effective date is less than on hand date. But I can not able to change On hand date since it is greyed out.

Please suggest how can i change on hand date.

Thanks,

Ray