When you print/plot and you gain control of AutoCAD again but can't plot again because it says there is a plot job in process, there is a setting that can help.
About the Background processing options for plotting:
If you turn on Background processing for plotting, then you gain control of your AutoCAD based program much quicker and the print/plot job continues to work in the background. However, the trade-off is that it takes longer to plot and you cannot send another print/plot job until it is done.
If you leave Background processing for plotting turned off, it plots quicker. However, you must wait for the entire job to be sent before you can do anything else in the AutoCAD based program again.
Go into Options and select the "Plot and Publish" tab
Either check or un-check the Plotting option under "Background processing options" (see fig. 1)
I recommend leaving it unchecked unless you have a lot of plot jobs to do quickly and you are unable to use the PUBLISH command to batch print/plot your jobs.