%Error opening tftp

%Error opening tftp

Need help again...
What could be the possible causes of the error below? There's no problem with the tftp server. Other devices were backed up without any problems while some backups generate this error. Thanks for your help.

enable
Password: **********
hostname#copy startup-config tftp
Address or name of remote host []? 10.x.x.x
Destination filename [nielgin-confg]? 38_ConfigFile.txt
.....
%Error opening tftp://10.x.x.x/38_ConfigFile.txt (Timed out)
hostname#









                New to ADManager Plus?

                  New to ADSelfService Plus?