F-02 (Vendor payment)

i want to post a Vendor payment with a transaction F-02 :

debit : vendor

credit : Cheques for cashing

but when i choose 40 as a key posting and "vendor X" as an account, i had this message : "Account "441115" in company code "M100" is marked as a reconciliation account for account type "K" and cannot therefore be directly posted to."

so how to choose a vendor?

that 40 is the good key?

and how to post this operation

i hope your help,

jehade