I'm having the same issue, but with a PureFTPd server. Not sure if older FlashFXP versions work, though. lftp (UNIX client) can connect fine. I can make a test account available if you need one
FlashFXP v3.0.2 (build 1045)
PureFTPD v1.0.20
[L] 200 PORT command successful
[L] LIST -al
[L] Connected. Negotiating TLSv1 session..
[L] 150 Connecting to port 10153
[L] error:1408F10B:SSL routines:SSL3_GET_RECORD:wrong version number
[L] error:14095044:SSL routines:SSL3_READ_N:internal error