Why is this an issue?

Indexed properties are meant to represent access to a logical collection. When multiple parameters are required, this design guideline may be violated, and refactoring the property into a method is preferable.

Noncompliant code example

Module Module1
    ReadOnly Property Sum(ByVal a As Integer, ByVal b As Integer) ' Noncompliant
        Get
            Return a + b
        End Get
    End Property
End Module

Compliant solution

Module Module1
    Function Sum(ByVal a As Integer, ByVal b As Integer)          ' Compliant
        Return a + b
    End Function
End Module