This error occurs when you try to add or subtract two Vectors that do not have the same dimensions.

To fix this, transpose one of both of the Vectors so that they are both the same dimension.

In this example we try to add (or subtract) two Vectors.

The same error occurs when subtracting:

The error occurs because W is a row Vector and X is a column Vector:

Solution:

Use LinearAlgebra[Transpose] to convert one Vector to the other Vector's type:

Alternatively, you can use one of the short forms for Transpose (^+ or ^%T):

For users of Maple 17 and earlier versions: These examples resulted in a different error message.  The solutions are the same.  For example, the example given above resulted in:

LinearAlgebra[Transpose], Vector