The error means that the entry in the sampler's interfaceName setting does not match the value in the interfaces file found in the SYBASE_HOME directory. Check the sampler and the said file, as well as the SYBASE_HOME environment variable of your Netprobe's startup script.
I'm getting the following error when I try to sample using SQL-Toolkit against my Sybase server:
Fail - ct_connect(): directory service layer: internal directory control layer error: Requested server name not found.(101188867)