Excel Combination Generator (overflow problem)

Hi everyone, i hope someone will be able to help me with this

i have a code that generates a permutation based on the inputs of 8 columns and concatenates the columns together. it works great so far but i came up with a problem. it works when more than 2 rows are filled. so if theres only one entry in row 10 for any of the columns from A-H it crashes. the rows are filled with A,B,C across all 8 columns, if column 8 only had A then it crashes

Any help would be great.

can anyone help?