Alarm the machine is saying check paper size and when we change the paper size to letter it automatically resets back to legal and will not print

Did you trying hitting an Ok button, green button, etc to confirm legal size paper, maybe it wants you to confirm paper size. Also legal is 8.5x14, did you select legal or enter the size as a custom page?

Printer wont stop paper, if any page length mismatch,Select page length as any size, as well as while shooting the print command select page length as legal & try it. I feel that teflon not rotating properly, result paper jamming at bottom end. If any paper length faulty printer detects the length give message of mis match..Pl check carefully...

HP Laser Jet 4100 HP Not pulling paper from Tray 2
Action: The 4100 will look at tray 1 first then tray 2 If tray 1 is empty it will pull from tray 2 if the papersize matches the job otherwise back to tray 1 and ask for the paper. Your machine likely thinks the paper in tray 2 is not the size you want. For instance you have LETTER in tray2 But the machine thinks it is legal. The LJ 4100 detects the paper size in tray 2 automatically. If you print a configuration page: MENU them INFORMATION then ITEM then CONFIGURATION PAGE then SELECT. The page will print and show what size paper the machine thinks is in Tray 2 if it says LEGAL and you have LETTER you need to Check The Paper Backstop in TRAY 2. The back stop sets the length of the paper if it is not at Letter (8 1/2 x 11) the machine will not detect LETTER. Even if it just a little bit off or between positions.
If it is set at LETTER then you may have bad switches in the machine that are operated by the tray. Or the arms on the tray that operate the switches are not moving properly. You will find the arms on the rt, side of the tray and feel them change position when you move the backstop.

Hope this helps helps. Please keep us updated and remember to rate this answer. TF

Open the manual feed tray and place the paper in. It should automatically feed from that tray.

The 4100 will look at tray 1 first then tray 2 If tray 1 is empty it will pull from tray 2 if the papersize matches the job otherwise back to tray 1 and ask for the paper.
Your machine likely thinks the paper in tray 2 is not the size you want. For instance you have LETTER in tray2 But the machine thinks it is legal.
The LJ 4100 detects the paper size in tray 2 automatically. If you print a configuration page:
MENU them INFORMATION then ITEM then CONFIGURATION PAGE then SELECT.
The page will print and show what size paper the machine thinks is in Tray 2 if it says LEGAL and you have LETTER you need to Check The Paper Backstop in TRAY 2.
The back stop sets the length of the paper if it is not at Letter (8 1/2 x 11) the machine will not detect LETTER. Even if it just a little bit off or between positions.

If it is set at LETTER then you may have bad switches in the machine that are operated by the tray.
Or the arms on the tray that operate the switches are not moving properly.
You will find the arms on the rt, side of the tray and feel them change position when you move the backstop.
Hope this helps.

HELLO! THE PROBLEM IS NOY ON YOUR END, THE MACHINE AT THE OTHER END HAS TO BE SET UO FOR LEGAL PAGES.SOME PEOPLE HAVE TRAY FOR LEGAL AND ONE FOR LETTER, THEN THE MACHINE WILL CHOOSE IT AUTOMATICLY. GOOD LUCK BROTHER TECH

When you say printing? Do you mean from the computer or are you making copies. If you are printing from the computer you need to change the paper size that you are printing to under the printers properties or the out put tray. If you are making copies just hit the reset button or just manually select another paper tray on the display pannel. Or if you have change a paper tray to leagal size change it back to LTR and make sure the paper is installed the correct direction.

You just stated the problem yourself!!!!!!!!!!!!!!!!!!!!!

Are you using Letter or Legal?? then the tray need to be set to that particular size.

If using Legal set to Legal, otherwise the machine will automatically know you are using the wrong size.

You have to go into the menu and change the setting to Legal.

here is the manual:

http://www.fixya.com/support/p202524-panasonic_panafax_uf_595_plain_paper/manual-7600/page-3