If K3B doesn't start to record with the error message "Could not determine size of resulting image file" and in the debug details the mkisofs/genisoimage tool is saying something like "genisoimage: Directories too deep for 'a/b/c/d/e/f/g/h' (7) max is 6.", you need to disable deep directory relocation:
Go to Settings menu in K3B, Configure K3B option, Programs section, User Parameters tab, edit the "mkisofs" line and add the text "-D".
If K3B doesn't start to record with the error message "Could not determine size of resulting image file" and in the debug details the mkisofs/genisoimage tool is saying something like "genisoimage: Directories too deep for 'a/b/c/d/e/f/g/h' (7) max is 6.", you need to disable deep directory relocation:
Go to Settings menu in K3B, Configure K3B option, Programs section, User Parameters tab, edit the "mkisofs" line and add the text "-D".
Note: This violates ISO9660