Cannot apply license in VMWare ESXi 5.5.0 after Evaluation Period has expired

Hi. I registered and downloaded VMWare ESXi and VSphere about 2 months ago and got it running on our server.

Today when I logged in with VSphere, it told me the evaluation period is over and I need to get a license.

I logged in to VMWare and checked the VSphere download link with the binaries for ESXI 5.5.0 and VSphere 5.5.0 and was told I had not registered for the product.

I registered for the product and the files became available and I also saw the license key at the top of the download area.

I copied the license key and went to VSphere, logged into my ESXi and clicked Configuration, Licensed feature, and Edit.

I Clicked Assign new license and pasted the license key into the box and clicked ok.

Then I clicked OK to close the 'Assign License Dialog' but it came up with and error "An error occured when assigning the specified license key: License is not valid for this product"

I have tried repeatedly and havent been able to apply the license.

Please help!