Cannot complete Paypal purchase

Installed the plug-in last night, connect to our sandbox and completed a transaction without any issue. However, we are getting this error when trying to complete the transaction at paypal this morning:

UserException: message ‘Exception thrown while routing to userauthserv and falling back to legacy not enabled. No way to create token’, return code: 4002 Backtrace: User::UserException::UserException(int, String const&) User::UserAuthManagementBLI::login_token_through_uas(User::UserAuthTokenVO&, bool) User::UserAuthManagementBLI::login_token(User::UserAuthTokenVO&, bool) User::WebSessionALIImpl::create_auth_token(User::AccountBDO const&, User::LoginBDO const*, bool, unsigned char) User::WebSessionPimpALIImpl::set_session(User::AccountBDO const&, User::LoginBDO const*, bool, unsigned char)
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I think we added a ‘Thank you’ callback page to the setting, that’s all. It is not working even without the callback page now. Wondering what is happening.

Can anyone help?

THanks!

http://ww.wp.xz.cn/plugins/wordpress-simple-paypal-shopping-cart/