A few comments:
- Setting the default PCL Symbol Set via the Embedded Web Server interface ought to set it as the user-environment (power-on) default, so if this only works for "the first one", this perhaps suggests that something else is at play here.
- You also say that you "... had a command line we used to do this on the previous OKI printers but it doesnt work for this printer ...". Just what was this command line, and what is the content of any file(s) which were caused to be copied to the printer port?
- I'm not sure how you are printing "... the bar code from my proprietary system ...", since (as far as I'm aware) the LaserJet M401 series does not include any printer-resident bar-code fonts (I may be wrong). It would usually be achieved by having a suitable bar-code font in an add-on hardware module (DIMM, SD-card as appropriate for device), or as a downloaded PCL-format soft font; both types should have a specific (and documented) font selection sequence required to select the fonts.