wifi error saying "kernel Error storing postMessage 74"

Yes! I found the ultimate workaround for this issue. Just get some USB wifi-adapter that adds an extra interface in the network preferences panel. Turn off the wifi interface of Catalina and select the network interface this adapter gives you. I am now back online. No need to downgrade the OS. Just some ugly, clumsy, cheap USB thingy dangling from a USB port. It is already stable for half an hour. If I don't come back here it probably continues to work well.

Nevertheless, Apple should fix this in Catalina!

Today I brought a Late 2014 Mac mini with Catalina to the office. The same issue!

On my way home I passed by a computer shop and bought a tp-link "AC1900 High Gain Wireless Dual Band USB adapter" which I also need in a certain room at home to improve reception.

Just installed it and it feels like an improvement in speed at home. Also, it uses a completely different network interface. You can also choose what kind of connection it is.

This might work. Next week I am in that office again and will report back.

oh, by the way. I tried fixing that Wifi-network. I found a network wifi-switch with a few dozen access points connected to it. The network admin left a note on how to reboot it in case of trouble. After waiting for the wifi-users to leave the office/going all into a meeting, I did a reboot by unplugging the thing and waiting for a minute and rebooting it. After a few minutes the wifi-networks where up and available (a blue light on those white discs on the ceiling). All machines reconnected automatically, except my MacBook Air with Catelina.

Will the update from 10.15.2 to 10.15.3 do the trick? Tuesday I will try it.

I gave up this morning after struggling for two hours with this. I just quickly popped out and bought a Thunderbolt 2 cable to connect to a nearby iMac 2011 with an old MacOS that did have a working wifi connection. At the end of the day I tried your suggestion with another, new user. Again, no connection. I switched back to the usual user account. Then I launched Wireless Diagnostics as you suggested, to try the tools in it. I had tried to generate a Diagnostics Report before, but that would make it hang endlessly. Just like trying to make a connection makes the wifi-menu hang.

This time all of a sudden my wifi connection started working again! Now on wifi in the train, which works flawlessly. Tomorrow another office, or a library, etc. No problems elsewhere.

At first I thought it was because of the Thunderbolt connection, but the Network Order had Wifi listed on top. I could disconnect the Thunderbolt cable while the wifi network connection would stay up! At least for half an hour, then I had to leave.

Will give an update next time I am in that office!

No luck on 10.15.3 either. Someone else also brought a MacBook to the office with Catalina. She is also in trouble.

I reported this at apple.com/feedback hoping it will make Apple look at this thread:

Exactly the same here! Turn off wifi for a little while, then back on and for a few minutes the connection works. And stops again. With the familiar error messages in wifi.log through Console:

"Error storing postMessage 74"

"Unexpected payload found for message 74, dataLen 104"

Only at work, but in many other locations with wildly different wifi setups it works.

Did you try installing WiFi_kexts as suggested by indomen on 3 November? I am hesitant because that seems like something Apple, not endusers, should fix if it requires going that deep.

Hi Thiago, can you connect to other wifi-networks without problems? Perhaps we can find similarities in the problematic wifi-networks we are trying to connect to.

I know that the maintenance of my problematic network is lacking. The company that services this network has not visited the building for at least half a year. It is a professional network with a few dozen nodes, access points.

Their reply to a request for service will be that my machine is the problem (one from outside, not under their service contract). None of the other employees have complaints after all.

Indeed, same situation. I also used a few Gb outside of my data bundle because of Personal Hotspot on my iPhone.

Can you include a picture of the access points? Perhaps that will indicate what brand it is. On the ceiling in my office I see those white discs with a little blue led indicating power. Will upload a picture later. I also have access to the room with all the networking and will find the brand of the hardware there.

Back in the office. The switch is from Unify. https://rrustema.stackstorage.com/s/srVCeCNqR6wTOiP and the access point on the ceiling looks like this https://rrustema.stackstorage.com/s/c8sWzGN1yLvthQ4

Strangely enough, I could transfer the pictures from my iPhone to my MacBook Air by connecting to the problematic wifi network and use Airdrop. That worked very briefly, then the connection stopped. Nothing works anymore.