Apparently it's a fairly common error. Use a pushpin or small paperclip to remove the SIM (top left hole above the SIM slot), put a couple layers of tape on top of the card and reinsert. I've had the same problem you reported, and this has seemed to fix the issue.
I did the same as Clarue42. I inserted a pushpin into the SIM card eject hole and popped it out, then re-inserted. I've always had the problem with the intermittent sim card errors, but the error would always clear itself within a couple of seconds. The reason I ended up on this post was because my phone was not clearing the error, even with a restart.
It's all better now.
Was having this same error and did a Google Search after checking here. Restart and simulated battery pulls did nothing to address the issue. The AndroidCentral forum advised simply using a pin to eject the SIM card (Upper left side of the phone, as your are holding it, on the side.) and reinsert it after a few moments. I followed this instruction and the error resolved itself. I do recall dropping my phone a few times over the weekend (Otterbox Defender case, so no damage) and would theorize that the SIM was somehow jostled and needed to be reseated. Will repost if the error returns.
I've had my One since release and I too have been having this issue. It seems to come and go at random. I don't recall anything specific happening to start the problem and I don't know what the phone does to "fix" the problem. I have read some other forums and this SIM card problem seems to be a some what common with HTC. Is it a SIM card problem? Is it a phone problem? Hopefully it will get addressed.
I actually picked up a new HTC One yesterday from the store. They decided to give me a new one. So far the SIM error hasn't happened on the phone. Unfortunately, I do have some new issues with this phone (death grip, raised glass causing a huge lip)
i havent see anything like this so far..could just be one of those random here and there issues that we are all used to seeing from time to time
I've been getting the same error. I've only had the phone about a week and I've seen the message the past couple of days. Today my internet connection was completely disabled. I went into "Settings" then "Network Mode". I changed Network to "Automatic" so I could pick up the 3G signal. After that I went to "System Updates" under settings and ran "HTC Software Update". The error message went away and I got my 4G service back... Hopefully this will fix the problem.
Did the recent update and it's still giving me errors. Curious to know if anyone is having these problems or this is just an isolated case with me.
I've had my HTC One for about a month now. Within the last week I've been getting a SIM card error message. It started as a once a day thing now its 2 to 3 times a day. Is anyone else experiencing this problem? I cant use the phone when this happens.