If you have a third party or unsupported SFP installed in your switch the switchport will go to err-disabled state. By running the command show interface status err-disabled you will see the reason is Unsupported SFP.
Obviously the recommended thing to do is purchase a valid, supported SFP that Cisco recommends so if you have any issues you can call them for support. If you don’t have one handy or the time, do the following.
Run the following command:
Do not try to tab-complete the command as it is a hidden IOS command. Type it in, hit enter, then you will see the following warning:
Warning: When Cisco determines that a fault or defect can be traced to
the use of third-party transceivers installed by a customer or reseller,
then, at Cisco’s discretion, Cisco may withhold support under warranty or
a Cisco support program. In the course of providing support for a Cisco
networking product Cisco may require that the end user install Cisco
transceivers if Cisco determines that removing third-party parts will
assist Cisco in diagnosing the cause of a support issue.
Furthermore, enter this command as well to disable the switch from putting the port into err-disabled state in the future:
no errdisable detect cause gbic-invalid