Currency roll up field is not working in Dynamics CRM

I've Bank and Bank Fee look ups on a custom entity call Line Items. Upon change of Bank fee lookup, I am copying fee value in a currency roll up field using javascript. 

Now, I configured currency roll up field on Bank form to aggregate all of the fee that is used for a certain bank. But upon refreshing the roll up field, it is throwing following error:

"Record currency is required to calculate rollup field of type currency. Provide a currency and try again"

I've added the base field as well on the Line item form but still unable to sort this out. Any idea/help on this?