Multiple Primary key

[getting_out]

Good evening people.

I'm trying to create a simple table via MySQl Navigator.
The table il structured in this way

dt_amt	Date		Not Null	Primary Key
oper	INT		Not Null	Primary Key
amount	Decimal(3,3)	Null		---

but when I choose "fire" it shows me a "multiple primary key defined"
message and doesn't make me create the table.

Isn't MySql able to handle multiple primary key or it's a navigator bug?
In the same day I can receive data from different operators.

Thanks in advance D.