If I insert a pdf underlay into a drawing, it won't display or print out. I know a pdf has been inserted as I can use Erase-All and it will say an object has been selected. The funny thing is that it all worked fine a week ago, and now doesn't. I can open a drawing done months ago which was fine but now there is no pdf displayed.
I've checked various settings against another computer and they are the same.
Just a shot in the dark here .... have you investigated the IMAGEFRAME variable?
Don't have ACADLT here to test with so hope this helps.
I've experienced the same problem in AutoCAD LT 2013. I insert a clipped PDF underlay and it shows as an empty box. Turning the image display on or off does nothing. Changing the imageframe settings affect the frame, but not the image which remains invisible.
After a lot of experimentation, I seem to be able to overcome this by copying the invisible PDF insert to a new location in model space, then without selecting anything toggling the IMAGEFRAME to 0 and then to 1. Once I get the image to display, I delete the new copy and try to save and print the visible image. If I close that file with the visible image and re-open it, the image is again invisible. So, I have to jump through the same hoops to make it show up again.
This visibility feature of the PDF underlay seems to have a flaky bit in the software that is being affected by something other than just the IMAGEFRAME command. It is definitely a bug that should be fixed as this feature is critical to electronic stamping of plan sets and the stamp shouldn't just disappear when you have a deadline looming and you can't get it to print.