So the symbolic in Mathcad 15 has a hard time to calculate the symbolic inverse using your new matrix SP and when it finally manages to do, the result of the single elements are so large that Mathcad refuses to display even when you try to display single elements only (at least that applies to the first three elements).
I guess that Mathcad 11 with Maple as symbolic engine is able to display the results, but I wonder in which way these huge results would be useful for you! So you either have to use another, more capable software or you rethink about what you actually want to accomplish.
If you later intend to provide values for all your variables, setting up the whole thing as a function in all those variables might be a solution. As the error message says, you can still use the symbolic results in further calculations, Mathcad just refuses to show them.
Mathcad 11, with the proper allowance for NODE_DISPLAY_LIMIT has no problems showing the combined result, let alone the individual parts.
(display was cut off midway of the second page, the total width of the full result spans about 48 pages...)
Note that it is not a feature of the symbolic engine ( Maple ), but of Mathcad 11, and 11 alone: it's not available in Mathcad 2001i, nor in Mathcad 12.
As the Display limit is in number of bytes, not in number of symbols, it may help to reduce the size of the names of the variables. So instead of: