Error ORA-3113 ( need help )

	I just install a oracle database on INTEGRAPH 6000 running on UNIX v7.1.3. I can use sqlplus to access the database,it work fine. But when I try to access it through sqlnet ( sqlplus login-name/passwd_at_t:hostname:oraid ), it give me ORA-3113 error message; This error message means that "an-end-of-file was processed on communication channel, but was not properly handled by SQL*Net software. This is an internal error message not normally issue". 
	I check my system, I find that the system here has multipleuser i_license, I also reinstall the sql*net and tcp( I relink the system after I reinstall )then it still give me 3113 after I try to access by sqlnet. 
	Does anybody have some idea !? I will very appreciate that. THANKS first

						Sincerely
							D. L.