Why was there controversy over the size of the land grant?

Because the early methods for allocating land were arbitrary, based on random choice or personal feelings instead of using reason or a defined system.

This caused claims and border disputes, besides, sale of public land turned into a means to generate profit for the government rather than encouraging settlement. Lands granted were sometimes huge, so  prices and investments needed for agriculture made it difficult, especially to small investors, to achieve their goals of working and living of them.  

b. the 200th birthday of the united states