After some thought I realized that I created my custom fields with a leading underscore, which was not an acceptede field for the OLAP Cubes. Once I corrected that I was able to add those fields onto the cubes.

Also, on a side note, we all know that there has to be a look-up value table associated with a Text Custom field ( and some other fields), to be able to be added as a dimension. However, since some of my fields has “multiple values” allowed from their lookup tables, these fields were not available under configuration of Cubes to be added as dimensions. Again, once I corrected ( painful!), we were OK.