I recently bought an EF70-200mm F/2.8L IS USM (USED), the lens tested on EOS 6D, 60D, and even A7III (With Sigma LA) it work well. But once I mount it on my Elan 7 it works fine for the first few shutters after a while doesn't know what happens the lens become disconnected, no longer able to AF, and the camera display will show [MF], then once press shutter the mirror will lockup and display blank left flashing Battery icon, press shutter again then mirror back to position, and the display is back but still show [MF]. Power off and on doesn't solve this issue, but unmount and mount back will solve, perhaps after while error comes back again.

My EOS 30 works fine with other EF lens, so i really don't know is bad lens, or bad camera.. hahahaha

I search online, some ppl said is battery contact issue, because with BP-300 will face this problem sometimes especially with AA battery.

Some said is shutter dirty cause of this, but the [MF] made me feel is related to the lens.

Anyone of you faces this problem before no matter on EOS 30 or any other EOS SLR, maybe can share your experience.

I suspect is the BP-300 problem, as I using AA battery and my BP-300 battery contact has some issue due to previous battery leaking. I tying to troubleshoot it by:-.

1. I bought CR123A battery (yet arrive)
2. Direct install battery without BP-300
3. Test the lens again.

If this cannot solve it, then I really don't know what should I do.

There are no FIRMWARE update for such SLR camera unlike Digital camera if let's say the lens is not compatible with the body. The body is Year2000, the lens is the Year 2001 I don't think it is not compatible. There are too many possibilities, however, i really want to solve this issue, because i bought this lens for the camera body, if it cannot be used then no point anymore.

I will share some picture or video of the camera~

Thanks

Not had that experience as I do not have that Camera Or that lens BUT I have EOS 100Fn + EOS 300v both 'Gift' cameras. I also have a SIGMA UC AF Zoom 70-210mm f4-5.6 which works on the 1000Fn but NOT on the 300v ! The 300v screen goes blank when Sigma lens is fitted !