Oracle Ora-12557:tns: The protocol adapter is not loaded ____oracle

Operating system: Windows 7
Database version: 11.2.0.1
Problem Description:
Directly through the Sqlplus SYS/ORACLE@10.10.100.109:1521/YSXT as SYSDBA can login, but through the Sqlplus SYS/ORACLE@YSXT as SYSDBA can not log in, reported ORA-12557:TN S: The protocol adapter is not loaded. Check environment variables Tns_admin, oracle_home are all fine.

Finally, check the environment variable path and find that both the client and server directories are added to the path and the client configuration is removed. As follows:

Solve:
In the PATH
F:\app\Administrator\product\11.2.0\client_1\bin; F:\app\Administrator\product\11.2.0\dbhome_1\bin;
To
F:\app\Administrator\product\11.2.0\dbhome_1\bin;