problems with null-valued expression error

I run my code that gathers certain parameters against multiple machines to create a report. I gather the parameters in a hashtable. Problem is when running the script against one of the machines which in theory should be identical like the others I get

You cannot call a method on a null-valued expression.

+$properties = @{

+~~~~~~~

       +CategoryInfo : InvalidOperation: (:) [], RuntimeException

       +FullyQualifiedErrorID : InvokeMethodNull

I checked all the variables that go to the hashtable and all return values unless I have some caching I'm not aware of. How can I pinpoint the one causing the error? 

yaro