obj.alternateColors is null or not an object

From time to time, when I load my grid page, I get a javascript error

'obj.alternateColors' is null or not an object.

Now this only happens outta the blue. I just reload the page, and it works. But for people that are looking at my grid, and they get the javascript error and the page does't load, they don't know what to do.

Is this a bug or something? why does it happen sometimes and not others?

Anyone get this at all? It drives me nuts because it only happends like once every few days.

So it's just my code that comes up with this error the odd time?

Dunno, I'm having similar problems, it's not just you...