Access share folder with error: No network provider accepted the given network path

My workstation have WIN and DNS but still cannot access \\servername\share with error message "No network provider accepted the given network path", but it work on ip address plus other servername.   example\\10.20.10.1\share it open with no error. \\servername\share open with error No network provider accepted the given network path. \\name\share open no error too.  why ?  note: servername:10.20.10.1 and name:10.20.10.1 too.

Thank you,

Reg,

wcnw