Excel 2010 formulas returning error because users accidentally entered a space in a cell.

I have prepared a census worksheet which contains formulas that refer to other cells.  From time to time, users tell me something is wrong with the worksheet because "####" appears in the cell where the formula result should be.  I have discovered that somehow they have entered a space in the cell that the formula refers to.  Once I delete the space, the formula returns the correct answer.

Is there a way to write a formula so that it it treats a cell that contains a space in it as if it does not exist?

I have attached an example..  in Cell T13 of the "DEC" worksheet, I entered a space.
I would like to prevent users from entering spaces in columns Q thru Y, or else adjust formulas so that spaces are not recognized.
Monthly-2014.xls