Solaris 10 comes with some of the more insecure access methods shut off by default. The error message tells you the START METHOD won't work. I.E.: telnet, rexec (rsh/rcmd), etc., etc..
Does your "X" emulator use SSH to connect ? The later versions of "Reflection X" can use OpenSSH to connect.
OR, on the Solaris 10 box, you can enable telnet, or RSH, or one of the other methods that eXceed allows you to use, as a means to connect to the Solaris 10 box.
As long as you already have the account on the Solaris 10 box, and you use a "connection method" from eXceed that is enabled on Solaris, you will be all right.