Most likely the OpenVPN server has started rejected your login details. However I'd recommend checking both the OpenVPN log
and the Console
to ensure that the Authentication Failed (AUTH_FAILED) message isn't appearing for another reason (the OpenVPN server can sometimes send an AUTH_FAILED message for a different reason).
Viscosity should be flushing the saved details in your KeyChain when that error message appears, so it is unlikely this is the cause. However you may like to ensure any old saved details have been removed from the KeyChain manually. Instructions for doing this can be found here
Otherwise I'd recommend getting in touch with your VPN Provider
to ensure your account details are still valid.