Recently this error started popping up as soon as open Unity with any project:
and
I am not sure what the cause is or how it will affect me.
I have the same error. Do you have internet at your location? It doesn’t happen if the internet is up, at least for me.
In my current location, I can’t have my internet running constantly, and it can be a little annoying to clear it every time. I don’t know a way how to get rid of the error, at least permanently.
So far, I haven’t noticed any effects that it may have caused.
With me the error has disappeared now. It doesn’t make a difference whether the internet is up or not. I have filed a bug report.
The same also for me… restarted unity, nothing changed. Any ideas? 
With me the problem re-appeared as well. Strange…
I have the same error.
for me it started when I started messy cross-patching between two svn-branches of my project. …
same here
have my project in a Dropbox sync…
I have noticed the same thing that upon having internet connection the error just disappeared.
Same problem here. Appears even on recently created projects. The error appears since the last update 4.2.0.f4
any solution for this? i also get this error;
Socket: unable to join multicast group, error: Operation has failed with error 0x2726: An invalid argument was supplied.
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Same here, can’t think of anything that would have caused this to start happening. Using Git for version control.
I also got this error. It seems to be come up somewhat randomly when opening Unity…a bug?
Am I the only one who still gets these 2 errors when starting Unity? (version 4.3.0f4)
Socket: unable to join multicast group, error: Operation has failed with error 0x2726
Unable to join player connection multicast group.
i get these errors on my machine that uses proxy and member of a domain. it is windows 8. do you have similar specifications?
I am now getting this error whenever I start Unity on my desktop PC. I have uninstalled Unity and reinstalled it, returned and obtained a new license, but nothing helps. While the error can just be cleared, it is preventing any project I load or create from working correctly. This is a very recent development. Nothing on my PC has changed since the last time it worked until now where it doesn’t work. Unity still works on my laptop, but nothing I do lets me open projects or create projects without getting this error.
I have restarted my router, restarted my PC, even tried to launch Unity in safe mode.
There were a lot of people having this same issue in this thread, but never any resolution. How do we fix this issue?
Worked fine two days ago, doesn’t work today. Windows 7 Pro, 8gb RAM, etc, etc, etc.
edit: I just returned my license key, then completely uninstalled Unity3d using Revo Uninstaller, then ran CCleaner until it came up clean, then deleted every Unity folder I could find on my PC, restarted my computer and reinstalled Unity3D then obtained a new license, and I get the same errors.
Two of them.
Socket: unable to join multicast group, error: Operation has failed with error 0x2726: An invalid argument was supplied.
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and
Unable to join player connection multicast group.
I can open the demo project Angry Bots 4.0, but the stage is empty, I still get the error, and the hierarchy starts empty even though all the assets are imported. As it turns out, I can reload the scene and it seems to work, but the error still happens every time I open or create a project.
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Chiming in. I, too, get this error opening any project file. Have internet access. OS X 10.8.5, Unity 4.3.4.
Ye, this is strange. I got these 2 error messages today when created new empty project without assets. Win7 with Unity 4.3.0f4, internet connection was working normally and there was no other computers at local area network at moment.
i also get this error; How to resolve this error?
I can’t believe this bug has still had no resolution. For the last year or so I’ve always gotten it. Every project. Every computer. Every copy of Unity. Every possible network configuration. Two different OS’s. These two errors are there every. single. time. I open up a project in Unity.
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I came here looking for A solution to the error messages below, but, it looks like there is none at this point.
Socket: unable to join multicast group, error: Operation has failed with error 0x2726: An invalid argument was supplied.
(0)
Unable to join player connection multicast group.
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