bar code printing problems

That would be the next step.

"Other than printer drivers does anyone have any thoughts."

What makes you think it is not the driver? I know there is a tick-box for HP printers for "Print true-types as bitmaps" option on one of the printer preferences pages - which helps when printing non-text. It may be worth seeing if there is that option on the printer you have

The size issue is valid, but there are business  reasons why they cannot be larger.

I think it may be the driver.  However on the Zebra Printer we have downloaded and installed the newest Zebra driver.  We have also checked against two printers.

I have not yet obtained the newest drivers for the Eltron and will do so.

I have no way of knowing how complex a bar code you are trying to fit into how many square inches.  But a 2 cubic foot box will only hold ...... 2 cubic feet.  For readability the very smallest element of the bar code needs to be at least several pixels wide, and from that basic requirement and the overall format of the specific bar code that you are using, there is a minumum number of total pixels required to print the bar code legibly.  If that number dictates a minimum total barcode width of, just for example, 2 inches, and you are trying to constrain the overall barcode to less than that, well, your chances of getting it to work reliably may be poor.  Keep in mind that the particular bar code that you are trying to print may not be -- and, in fact, probably isn't -- the least readable possible information.  That is, while all UPC codes are 12 digits, the pattern of bars produced by some 12-digit UPC codes are a LOT less readable (by the bar code scanner) than the patterns produced by other numbers.  For your product, and for reliability, you need to arrive at a solution that not only works reliabily and consistently, but which does so with the "worst case" bar code pattern.