I have been working on a Magento project and stuck on this error for a long time, I have tried to find the solutions in magento commerce forum, was struggling into codes and nearly modified all the paypal express checkout whole code.
But after sometime I decided to check the the backend setting again. So I did checked and found the solutions to it. Basically its a logical error with simple option to check. Here is how you can get rid of this logical error.
Step 1 : Login to Dashboard
Step 2 : Go to System –> Configuration
Step 3 : on Left hand Navigation, click on Sales –> Checkout
Step 4 : Allow Guest Checkout to “Yes”
Step 5 : Save
Basically its very simple but it did bugged me for quite some time, So I hope if you have such issues then this might help you.
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