I have a Canon EOS300D along with the 18-55 lens that is supplied as standard. I also have an additional lens, a Sigma 70-300mm F4-5.6 DL Macro. I bought this lens 6 or 7 years ago and it has been very lightly used on my Canon EOS500N. When I first got the camera I tried the 70-300 and it worked. Now when I fit this lens and switch on the camera, all I get is an error message, err 99 I dont get this error when I use the 18-55mm lens. It says in the manual that this error will show when something other than the other listed errors has occured Has anyone got any ideas about this ??