You cannot call a method on a null-valued expression. (Invoke-PasswordSprayOWA)

[Fahad0x9d3]

when i do this command : ( Invoke-PasswordSprayOWA -ExchHostname mail.**.com -Domain *** -UserList .\user
s.txt -Password ** )

return :

[] Now spraying the OWA portal at https://mail.****.com/owa/
[] Current date and time: 10/24/2017 23:36:44
You cannot call a method on a null-valued expression.
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
+ PSComputerName : localhost

You cannot call a method on a null-valued expression.
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
+ PSComputerName : localhost

You cannot call a method on a null-valued expression.
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
+ PSComputerName : localhost

You cannot call a method on a null-valued expression.
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
+ PSComputerName : localhost

You cannot call a method on a null-valued expression.
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
+ PSComputerName : localhost

what should i do to resolve this issue.

[Fahad0x9d3]

PSVersion 5.1.15063.674