Reset Error

When I reset my model, "sometimes", which means not always, it throws following error message.

Time: 0.000000. The label referenced at rank 1 does not exist on (null)

I checked all my labels, but no clue what is missing. Also, the issue is I can't duplicate the error(?) message (I don't know this is an actual error or not, though ). It seems to me that it happens randomly. Of course, there must be a reason, but it just makes me lost to find out the cause of "SOMETIMES" error without consistent happening.

If I ignore the message and run the model, it also throws bunch of exception errors on every where that works perfectly fine in the previous run. I really don't know what I did worng to make the "sometimes" error.

Anyone has an experience of the same or similar issue? What is the typical cause of this reset message? Where should I start to check for this type of message? I use version 5.0.4.

Thanks,
Sung