I have a 3550 behind an ASA. I can ping the latter from a station in the DMZ but telnet works from time to time and fails from time to time.
Other switch under the same domain of type 2960 or 3560 are fine.
I am having the same problem with 2950 switches.
However on the LAN, it is fine ping and telnet is ok.
I see no routing issues on the ASA, only gives SYN timeout