Yes, I can tell you what triggers it, as I just got that same Limitation today. It was triggered because PayPal detected that I was using an "anonymyzer," as they phrased it. Now, the word "anonymyzer" isn't even a real word, but that is what the customer service representative called it, and they were referring to the fact that I use Ghost Surfer to mask my IP address from the entire world through a proxy. It sounds like Paypal keeps getting better and better detection methods every day.
After I called in, though, they have reviewed my account and restored it.
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