Matrix must have the same dimensions (number of columns and rows) - ERROR

[Javi]

I am trying to solve this equation system and I am getting the below error: 

I have checked that all the matrix are 12x1  but I still get the same error. Can you please help me? Thank you very much in advance. 

[Werner_E]

Looks like you are working on the same homework as the poster here -> https://community.ptc.com/t5/PTC-Mathcad/PLS-HELP-Error-with-the-arrays-at-system-of-equations-dealing/m-p/657230/highlight/true#M189372

and are doing similar errors.

Keep in mind that its usually hard to impossible to debug just a picture. Picture are fine but always also include your worksheet here!

Best guess is that you typed square brackets. Square brackets create a matrix and so you possibly created a 1x1 matrix containing one element which is a 12x1 vector. Get rid of all the square brackets - most of them sure are not necessary anyway and if you need them, use parenthesis only!