Henry VIII's foreign policiesWatch
"How far was financial weakness the most important reason in bringing about failure in foreign policy in the period 1509 to 1529?"
So far all I have is that Henry lacked the financial funds to back Charles V when he finally invaded France which isolated him from claiming Pavia and the treaty between Spain and France.
However, I have no other further points and have no clue how to counteract this view
One way to counter the view that financial weakness was the most important reasons is saying what caused this financial weakness. I would say that opposition within England would be responsible for this and focus on the opposition to the Amicable Grant and link that to Henry's failure with the point about Pavia that you mentioned.
Lack of men? In 1512 (or around them, I'm not sure of the exact year) when he tried to invade France he was dependent on Spain to back him up, which they failed to do so he failed to win the war.
If you know enough about it then technological weakness may be a factor you could use (although that is also linked back to financial weakness as it is lack of money which caused his technological weakness).
Also, another factor could be his lack of success itself. To have success you could argue that you need a previous success to give you the reputation to enable you to negotiate from a position of strength (e.g. Henry V's conquering of Normandy was achieved only after his success at Agincourt). Henry VII had needed to focus on establishing his rule within his own country and getting rid of pretenders to the throne as he was essentially a usurper so Henry VIII was attempting to go from England being an inward looking country to a European power and this is a difficult transformation to make in such a short space of time.
Sorry I couldn't be any more help but hopefully this will give you some more ideas.