As all tamron lenses i used. it stops working in the middle of shooting!!?

You can order the Tamron 2x teleconverter here. Be aware that not all lenses are compatible with teleconverters, and you can actually damage some lenses by trying to use them with a teleconverter.

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Err 99 could mean several different things, such as... Memory Card, Lens or Lens contacts....

Here's what you can try:
Remove the memory card an enable "shooting with out memory card" and see if you still get the error. If it works your memory card is bad. Try another lens if you can. Clean the lens contacts with a pencil eraser (be careful not to get eraser dust in the camera body or in the lens). Worst case scenario is, Err 99 could be related to the shutter failing which would mean a trip to Canon.
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hi, clean the camera contacts also , change the firm ware of the lens , hope this helps

error 99 may be the only error that the camera can identify with the problem. Generally this is dirty contacts in the camera and on the lens. The fix is to rub them with a pencil eraser and ensure no rubber swarf gets inside the camera. ( Hold upside down and use a blower and brush for cameras after doing it. Do the same to the lens contacts and re position turn on camera and see if it works ok now.
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Hi turn on the camera with the lens on set to tv and a iris of f22 and use the stopdown button if the lens stops down the lens is ok if not the lens is faulty may need a intuper replaced

lens flexible pcb broken change it

Try gently cleaning the electronic contacts on the lens's mount with an eraser. This will remove any mild oxidation on the contacts. If this doesn't resolve the problem, then contact Tamron and ask if there are any issues using this particular lens with a Canon 40D.

Alan, Does one of the lenses have a solar or polarized filter on it?  It sounds basic but it would alter the type of light brought into the camera, that is a nice lens.  Are you shooting the smae F-stop for both side by side photos?  The 70-210 is a 3.5 or 5.6 right? Just a thought. randy320sgi

This is usually a torn flexible circuit or binding aperture in the lens. It'll have to go to a repair shop for replacement. About a $80 job.

You're probably right about the lens. Tamron lenses have a flexible circuit that drives the aperture blades. The aperture might need to be cleaned or the flex might be worn out. Either case needs a repair shop to correct.