What is a subject-verb disagreement?
Subject-verb agreement is when the subject and the verb agree in number/plurality.
On the other hand, subject-verb disagreement is simply the lack of that agreement. So, one way we can look at this is by negating a case of agreement.
The banks store money.
Banks is the plural subject. What do the banks do? They store, so "store" is the plural verb associated with the plural subject. What do they store? They store money, so "money" is the object.
(As a side note, that makes "store" a transitive verb, because it acts on an object.)
In subject-verb disagreement, you could see:
The banks stores money.
The bank store money.
The first one places a singular verb after a plural subject. The second one places a plural verb after a singular subject.
Hence, there is a disagreement in number/plurality.