Failed sending heartbeat to server

Hello Vaadin Community,

i just converted my large Vaadin 6.8.12 project into a Vaadin 7.1.0 project and everything was working decently well.
Now i noticed that whenever i reload my app using ?restartApplication or using my logout button (sets the Location/Url to the same page/reloads the page + closes the VaadinSession) an error pops up in my console saying: Wed Jul 24 08:48:20 GMT+200 2013 com.vaadin.client.VConsole SEVERE: Failed sending heartbeat to server. Error code: 0 When i then interact with the app (e.g. by clicking a button) i get a Communication problem-Notification and i have to reload the page. After i reload the page multiple times without ?restartApplication the heartbeat starts working fine again.
Is this a bug or did i do something wrong when converting my project?
I made this thread because i couldn’t find another one mentioning this Error.

Regards,
M R

EDIT: After i worked on another project and then came back i now can’t manage to reproduce the error like i could before. It doesn’t show up. Nevertheless i would like to know if maybe this is a bug or an issue that some other people also noticed.

Hmm… Sounds weird. Error code 0 is supposed to mean that the connection could not be established - usually that means that the server or network is down.

Thank you for your reply Johannes.

I think my tomcat had a little problem which resolved itself because when i worked on another project and then came back i didn’t encounter this error again (Only when the server is down but i guess that’s normal).
I will keep trying and if it happens again i’m going to try to make a reproducable test case, although i think it was really just a problem with my server as i wasn’t able to get the error after switching the project and then switching back, no matter how hard i tried to.