Barcode printing issues used to come up weekly where I used to work... it's been a while since I've dealt with one, but I do recall that printing from LOCL often resulted in problems - we usually had to create a specific printer in SAP pointing to a Windows or UNIX queue using the U or S access method, and making sure we got the right device type...
Firstly though I'd ask these questions of the user: has he been able to do this before, or is this new? If he has, what has changed - was it definitely using LOCL before? Perhaps something changed on the queue at the end (i.e. Windows drivers)... can his colleagues do this (are they using a different method, i.e. U or S)? etc...