paypal sandbox processing error-

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Over the weekend, our paypal sandbox environment used in our asp.net application suddenly stopped working. It had begun returning a \[code\]Could not create SSL/TLS secure channel.\[/code\] error when attempting to simulate a customer charge, on the \[code\]GetTransactionDetails\[/code\] call (which is after the actual charge occurs). I thought that perhaps the test API signature expires or something, so I went and reset our test account on the API website, and got new api values. Now, when attempting to simulate a customer charge, I get a \[code\]10001 internal exception\[/code\] on \[code\]DoReferenceTransaction\[/code\], where the actual charge occurs, and cannot even reproduce the ssl error. I have verified that the sandbox username, password, and signature are correct, and that the test credit card numbers are valid, and of course that the environment is set to sandbox.I have also verified that the test account is set up as a verified seller. Did anything change that could cause all these sudden problems?Our live payments still work, but this greatly affects our testing environment.