I'm having the same error, well not the exact same error, but it started this morning when trying to checkout via PayPal, it just went into a continuous loop, but it only happens on eBay.com.
So what I did was pay for my item via eBay.au (Australia) and it worked flawlessly, others are using alternative ways such as eBay.eu (Europe) and eBay.ca (Canada) which has worked for them.
Emptying the cache and changing browsers ain't doing **bleep** and hasn't rectified the error for me but paying on a sister eBay sight did.
Try that and see if it works for you.
