Assigning Value To InnerHTML Of Element

I have a situation where I'm trying to assign a value to an elements innerHTML. When I do this, the value is assigned, but it causes havoc on subsequent javascript calls.I realize this is kind of vague but I'm at my wits end on what to do. I've tried assigning the innerHTML value "NA", just plain text, and it has the same effect.Without being too confusing, I have a table of data inside a <div> where the user can navigate up/down by pressing the <enter> key, pg up/pg dn and arrow up/arrow down. When they move from record to record, I'm highlighting the new row and "de-highlighting" the old row. The row has many fields but only one fill in field which is where the user enters the quantity of the item to be ordered. This is on a local network using the Firefox browser.

Without the above line, all is well. When I use the above line, it messes up the highlighting of the row but also makes the fill-in field "appear" disabled. What I mean by that is when you type a number, you don't see the value change (even though the field has focus and the value is selected) but once you leave that line, the value you typed then appears in the fill in. Normally the value will change as you type a new value.