Hi Keith
Sounds like a communications problem with your mount. It could be in the ascom driver, but just as often it's a bad cable or physical connection. you might try ensuring you have the latest drivers and doublecheck/replace cabling
see the troubleshooting guide,
the specific passage here:
ASCOM AlertsWhen you first connect to a mount, camera, or other ASCOM-controlled device, you may see an alert message saying that a required capability is not supported by the driver. One example would be lack of support for pulse-guiding by an ASCOM telescope/mount driver, something that can occur with outdated drivers. In these situations, your only recourse is to update the ASCOM driver. These drivers are generally available from the ASCOM web site or, in some cases, from the device manufacturer. As a rule, the best practice is to use the latest versions of these drivers so you don't encounter problems that have already been fixed.You might also see other alert messages associated with the ASCOM driver for the mount:1. "PulseGuide command to mount has failed - guiding is likely to be ineffective." This is usually caused by a bug or timing sensitivity in the ASCOM mount driver, and there is generally no way to know if the guide command was executed properly or not. If you rarely see the alert and your guiding results are acceptable, you can probably ignore it. Despite the alert condition, PHD2 will continue to issue guide commands, so you don't need to take any immediate action. If you see the alert frequently, you should send us your debug log so we can understand the details of the problem and possibly help you describe it to the author of the ASCOM driver.
2. "Guiding stopped: the scope started slewing." This is pretty self-explanatory, but the determination that the scope was slewing is something reported to PHD2 by the ASCOM mount driver. Whether it was actually slewing isn't known to PHD2. Assuming you didn't mistakenly slew the scope with guiding active, there is probably a timing problem in the driver. If you want to sidestep the problem temporarily, you can disable the logic to check for slewing - go into the 'Guiding' tab of the Advanced Settings dialog, and un-check the box that says "Stop guiding when mount slews." This will let you continue guiding, but the results might be suspect. The debug log should provide the details needed to describe the problem to the author of the ASCOM driver.