The POSIT field shouldn't be 1 + the highest number in the table. The POSIT field is the number of the dimension.
For instance, you're trying to add 0CUSTOMER__0ACCNT_GRP to the cube. This would go into the same dimension as the parent InfoObject, which is 0CUSTOMER. Looking at your data, the POSIT for the 0CUSTOMER field is "0002". So the POSIT for the new nav attrib should also be 2, not 3.