The addition operator is trying to add matrices that do not have the same number of columns. Perhaps you mean to use the concatenation operator:
use = old_use[1:100, 1:50] || old_use[1:100, 53:57] || old_use[1:100, 59:75];
If so, a more efficient method is to form a vector of the column indices and then do a single extraction:
cols = (1:50) || (53:57) || (59:75);
use = old_use[1:100, cols];