On dragging an attribute into filter section, the entire filter section disappears. What could be the reason?

On dragging an attribute into filter section, the entire filter section disappears. What could be the reason?

One of the possible causes: --------------------------------------- Verify the parameter name used in the attribute. For e.g. Credit Customer_CUSTOMERPRICEBOOK" should be defined as "Credit_Customer_CUSTOMERPRICEBOOK". Ensure that all parameter names are defined with an _ (under score) instead of a space