OK, here are a few things to try, in this order:
1) Drop the quotes around your -BkExt parameter value:
Change this: -BkExt "BAK"
...to this: -BkExt BAK
2) Specify a backup directory after your -BkUpDB parameter, like this: -BkUpDB F:\SQLBackups
3) Try changing -DelBkUps 1WEEKS to -DelBkUps 7Days
Also, I find it helpful to use the -CrBkSubDir, so that all my database backups are organized in different directories.
And again, save the output from your job to a file, so you can trap all the errors and messages that are generated.
If it's not practically useful, then it's practically useless.