paypal sandbox unable to process request

I've been working and testing the sandbox system paypal uses.

It have been confusing, I've created some testing accounts. At the moment I've created a form from my site. A "Buy now" button.

It's works as it should:

<form id="checkout" target="paypal" action="https://www.sandbox.paypal.com/cgi-bin/webscr"  method="post">

    <input type="hidden" value="myemail@myaddres.com" name="business">
    <input type="hidden" value="Order" name="item_name">
    <input type="hidden" value="1000" name="amount">
    <input type="hidden" value="50" name="tax">
    <input type="hidden" value="SEK" name="currency_code">


    <input type="hidden" value="namehere" name="first_name">
    <input type="hidden" value="lastnamehere" name="last_name">
    <input type="hidden" value="emailaddressaere" name="email">

    <input type="hidden" value="addresshere" name="address1">
    <input type="hidden" value="cityhere" name="city">
    <input type="hidden" value="SE" name="country">

    <input type="hidden" value="0" name="address_override">


    <input type="hidden" value="http://www.mydomain.com/thanks" name="return">
    <input type="hidden" value="http://www.mydomain.com/checkout" name="cancel_return">

    <input type="hidden" value="uniqueid" name="invoice">
    <input type="hidden" value="sale" name="paymentaction">

    <input type="hidden" name="cmd" value="_xclick">
    <input type="hidden" name="charset" value="utf-8">

    <input type="submit" value="Buy" />
</form>

I'm sure (I think I'm) that the HTML is right (just that the inputs should end with /> )

Well, at paypal, I login and confirm the payment. Everything works great until I confirm it then the weird stuffs keep happening every time. So when I confirm the payment this is what happends:

Your account information has changed. Either you clicked "Pay" more than once but the original transfer was already made, or you just received money. To check, please view your account History and make sure you want to perform this transaction.

AND:

At this time, we are unable to process your request. Please return to facilitator account's Test Store and try another option.

Now after all this, it seems that the no payment was made, but the case is that a payment has been sent to the "business email". I just login with it, but there I have to confirm the payment.

Why is this happening? Why isn't it being confirmed?

I just started with paypal today. I've been fighting with it the whole day long (+night) Now I just had to ask.