Supinated Grip Pain

I am very new to GB and have been focusing on prerequisites before I progress any further. Recently, I have been performing a supinated grip hang to build strength before moving onto the german hang. However, My left arm appears to not rotate far enough to enable my hand to be in line with the bar and causes discomfort in the forearm. 

 

Is this a shoulder mobility issue or weak joints? How would I resolve?

 

Many thanks.

?? Have you just posted your question in 3 new threads??? 

Not cool.

I have the same problem I guess just look up some shoulder flexibility threads in here and do them all!  or hopefully someone will actuall give some insight  to this particular problem.

And has that alleviated some of the problem?