The Articles of Confederation created a federal government that was weak, in comparison to the power of the state governments. The founders did not allocate certain powers to the federal government that are crucial for running a government. An example of a necessary power not allocated to the federal government is the ability to regulate trade. The power to regulate trade includes the ability to tax and apply duties to goods that are being traded, thus providing income for the government.
Additionally, because states could each formulate their own trade policies with foreign nations, conflicts broke out between states. One state on the coast might refuse to trade with England and close its ports to English ships, for example, and the state next to it would see an economic opportunity and open its ports and trade with England, thus profiting at the expense of the neighboring state. These types of conflicts were common, and very bad for international trade. Foreign countries hesitated to trade with the states, due to the uncertain atmosphere. Simultaneously, states would set high duties or tariffs on goods coming in from other states, which resulted in a near freeze in trade between the states themselves. States would retaliate against other states who placed high tariffs on the importation of their goods by placing high tariffs on the goods from the offending state. These are the economic quarrels referred to in your question.
As a result of the mess created by the inability to regulate trade and the inability to levy taxes, the Constitutional Convention was called, and the Constitution was written to correct these oversights.