This is most likely a compatibility problem with an older third-party Sigma EF lens, not the camera body.

Older Sigma lenses are known to work on some film-era EOS bodies but fail on newer Canon DSLRs because their electronics don’t fully match Canon’s later lens communication protocol. A common symptom is exactly what you describe: autofocus may work, but the camera throws Err 01 when it tries to control the aperture during exposure.

First, clean the electrical contacts on the lens as well as the camera mount, since dirty lens contacts can also trigger Err 01.

If cleaning doesn’t help, the lens is probably electronically incompatible. In that case, there usually isn’t a simple camera setting to fix it. Practical options are:

• have the lens rechipped/modified if a compatible service exists
• use a different lens
• use it only if a specialist adapter/converter solution is available

So: try cleaning the lens contacts first, but expect the real cause to be old Sigma-to-newer Canon communication incompatibility.