Is this a new setup, or maybe a new problem?
It's likely caused by one of two issues;
1. The Explora is well known to be more sensitive to signals, your dish / LNB alignments could be partially out. Would still give good enough HD PVR signals.
2. A poor cabling or connection problem somewhere.
Of course there are other possibilities, but these are most common and it is installation related most of the time.
Please post the signal strength AND signal quality for tuner 1 on the Explora when this error occurs.
Someone will take it from there and guide you step by step, but as it's the weekend it could be a while. All the best with it.