It's good to know that it's just a coincidence. I was thinking that the Uptime tab was the same as this uptime.com process that is checking the sites within the My Web sites section especially since it's only those sites (I have other sites). I have sent them a message and will let you know what they say.
In my Google Analytics I could see the site uptime.com sending traffic to [all] my sites ... so I assume that this was part of the Uptime feature within the tab of the My Web sites section of your Web site?
Is it totally unrelated?
I will send a question there as well.
It comes up in the debug.log file ... hundreds and hundreds of rows. I am not confident if I should retain the plug-in or find another one if it keeps churning out errors. If the developer could advise urgently would appreciate as the file size keeps growing with the same error message.