Installed the Bitcoin QT client only last week... synchronised it with the blockchain... and sent my bitcoins to this adress... Now, when I want to send to some other address, it asks for the passphrase. However, have never had the option of providing a passphrase. Any thoughts on this?
However, have never had the option of providing a passphrase.
You must certainly have set a passphrase in the past. There's no way to remove it without knowing exactly what it is. If you can not recall what password you set, your funds are lost.