When I load my film the display says err - Nikon N50 35mm SLR Camera

It means either your film has reached the end, the film is jammed and cannot advance or the film is improperly loaded. The film leader may have slipped from the sprocket or broken,

What speed film? Does the roll have the DX markings (the black-and-silver rectangles)? If it doesn't, what happens if you set the film speed manually?

Is the ERR blinking, and is there an additional blinking E on the display? If so, the film is not loaded properly.
The film is supposed to advance all the way to the take-up spool upon loading. The camera then "rewinds" one frame at a time as you take pictures. This way the camera knows exactly how many shots are left on the roll. Also, if the back is accidentally opened, the shots already taken are already in the can and won't be ruined.
If you need a manual, you may download a copy here.
Try cleaning the battery contacts and see whether the battery reads full with no film in the camera.
If problems persists, feel free to reply to this post and give any additional details.

From the manual:
"If the error display is not canceled when the shutter release button is pressed again, insert the Dark slide, half-press the shutter release button while pressing the roll film holder's manual film advance button to wind up the film, then contact your nearest Mamiya agent or service center."

If you need a manual, you can download one from
http://butkus.org/chinon/mamiya/mamiya_645af/mamiya_645af.htm

how to make multi region of my dv-sp406

Jim, it really sounds like one of threethings. Either will require a repair shop.
1. the film sensor is not recognizing film in the film chamber, or film across the back, therefore not telling the advance motor to advance film...
2. The film advance motor itself needs replaced.
3. The rear door latch switch needs replaced.
Since everything else seems to do OK, I doubt the main computer board is bad.

Is the film loaded correctly? Have you tried reloading it? Also is it flashing DX too? That would mean the film speed is not DX coded so you need to set the film speed manually.

I had the same problem, what I did was set ISO to manual,and still got the Err,but I took a shot and the film advanced and it seems to be ok now.

does anybody know a freakin solution????

Needs new batteries, or the film isn't loaded properly. Check the battery area for rust too and clean the contacts gently with a pencil eraser.