WitnessServerinUse field reports InvalidConfiguration

Hi;

I am running two Ex2013 Std server in DAG mode, recently I found that the witness share in use has problem, when I run

get-DatabaseAvailabilityGroup -Identity EXDAG -status | fl

I got this....

WitnessShareInUse                      : InvalidConfiguration

Name              : EXDAG
Servers           : {EX02, EX01}
WitnessServer     : dc01.company.com
WitnessDirectory  : C:\EXDAG.company.com
WitnessShareInUse : InvalidConfiguration

I browsed internet for two days but cannot find a solution that fit me.  What should I try?

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KW - CNE,MCSE,VCP5