During the day of GBICs, 3rd party interfaces usually worked. Enter the SFP. Here's a typical response from a 3750 when plugging in, say, a Finisar SFP:
Feb 27 00:01:47.952: %GBIC_SECURITY_CRYPT-4-VN_DATA_CRC_ERROR: GBIC in port Gi2/0/1 has bad crc
*Feb 27 00:01:47.952: %PM-4-ERR_DISABLE: gbic-invalid error detected on Gi2/0/1, putting Gi2/0/1 in err-disable state
and a show int status demonstrates this:
show int status | inc Gi
Gi2/0/1 err-disabled 1 auto auto unknown
As an unspported work around work around, you can tell the switch to ignore the fact that the SFP was not blessed by Cisco. Keep in mind that Cisco will likely tell you to put in Cisco branded SFPs and that they won't support you with 3rd party SFPs in place (i.e., this is at your own risk!)
service unsupported-transceiver
no errdisable detect cause gbic-invalid
You'll see this message
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.
If you then move the SFP to another port, you should see something like this in int staus:
Gi2/0/2 connected 1 a-full a-1000 unsupported
It works... don't forget to do a write mem.