CDP needs to be disabled on the interface generating the error. What happens is ESXi is running the native switch of OS causing these errors. IE: (%CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/0 (not full duplex)
To fix this little issue run the following on the interface in question.
"NO CDP ENABLE" for newer IOS versions "NO CDP ADVERRTISE-V2