I think this or a variation thereof helps you out:
Issue
You want to turn off the plot warning that is displayed when the printer is not configured in the system.
Solution
To prevent the plot warning from being displayed, you can create a DWORD-value key in the Windows Registry named PLQUIET and set its value to 1. Follow these steps:
Click Start menu (Windows) > Run.
In the Run dialog box, enter regedit
In the Registry Editor, navigate to the following key:
HKEY_CURRENT_USER\Software\Autodesk\AutoCAD LT\R14\ACADLT-7001:409\Profiles\<<Unnamed Profile>>\General
Note: The values "R14" and "ACADLT-7001:409" will vary according to the product version and language. This path is for AutoCAD® LT 2009, English version.
Create a new subkey named "PLQUIET" under the General key by clicking Edit menu > New > DWORD Value.
Double-click the PLQUIET key.
Enter 1 in the Value Data box and then click OK.
Close the Registry Editor.
Warning! Problems caused by improperly editing the Windows registry could render your computer operating system unusable. Microsoft provides a wealth of critical information that you need to know about the registry in the Microsoft Knowledge Base.
Use the Microsoft® Registry Editor only at your own risk and only after backing up the registry as well as the system.dat and user.dat files as outlined for your operating system in the Microsoft Knowledge Base and in the related Autodesk solution TS66513. Additional information about the registry is also contained in the Help topics in the Microsoft Registry Editor.
