I´m rather new to QGIS.
So the issue is this. I downloaded some terrain data from INEGI (Mexico´s Geographic Information Institute) which contained the contour slope.
I had no issue doing it with the original data downloaded from the site, I had the info and followed this simple tutorial to get the Interpolation Raster.
I had proceeded to join 4 maps using Vector->Data Management Tools-> Merge Vector Layers and had no problems after the merge.
Having merged for maps the resulting map came out to be rather large for an interpolation and for my project I needed high resolution. So I need to clip a section of those slope maps to generate a raster of only a part of the map.
So I did that, I created a new ShapeFile layer and created a rectangular polygon that determined the area to be clipped. Then I went ahead and used Vector->Geoprocessing Tools-> Clip.
Having done this successfully I went ahead and used the exact same procedure to Interpolate this new slope and the error message I have been trying to solve for the past 3 hours appeared. "wkb access out of bounds".
This problem is exclusive to the "Triangular Interpolation (TIN)", Interpolation Method. While troubleshooting I tried the "Inverse Distance Weighing (IDW)" method which calculated somewhat successfully but with unsatisfactory results.