Kiattipong_Ballba,   Would you confirm a couple things for me? Do you see the same thing after restarting the switch? Have you checked to see if there is already a set for VLT, and if so have you tried removing any of the old ones?   Lastly, is the switch currently up to date on firmware?   Let me know and we can go from there.    
We need to config interface port-channel114 to S5248F = 2 Units with VLT for example interface port-channel114switchport mode trunkvlt-port-channel 114 But put the command then show error Dell-SW01(conf-if-po-114)# vlt-port-channel 104% Error: Internal error   Please help me get the solution. Thank you.
S5248F can not Config vlt-port-channel xx % Error: Internal error