Error downloading http://downloads.arduino.cc/packages/package_index.json
when i open board manager on my Arduino IDE, This error occurs.
I have tried this
Open command prompt (windows start button, type cmd in search)
Click top left of command prompt, click properties, enable quick edit mode
Copy: setx _JAVA_OPTIONS -Djava.net.preferIPv4Stack=true
Right click on command prompt, should paste
Hit enter.
But it didn't solved the issue.
Please Suggest what else could be the reason.
Do you have any other text in boards manager eg. for ESP boards ?
After you get that error there should be a bunch of red text in the black console window at the bottom of the Arduino IDE window after you close Boards Manager. Please copy all that text and then paste it here using code tags(</> button on the toolbar).
Error downloading http://downloads.arduino.cc/packages/package_index.json
java.lang.RuntimeException: java.lang.Exception: Error downloading http://downloads.arduino.cc/packages/package_index.json
at cc.arduino.contributions.packages.ui.ContributionManagerUI.lambda$onUpdatePressed$0(ContributionManagerUI.java:151)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.Exception: Error downloading http://downloads.arduino.cc/packages/package_index.json
at cc.arduino.contributions.DownloadableContributionsDownloader.download(DownloadableContributionsDownloader.java:113)
at cc.arduino.contributions.packages.ContributionInstaller.download(ContributionInstaller.java:334)
at cc.arduino.contributions.packages.ContributionInstaller.downloadIndexAndSignature(ContributionInstaller.java:309)
at cc.arduino.contributions.packages.ContributionInstaller.updateIndex(ContributionInstaller.java:287)
at cc.arduino.contributions.packages.ui.ContributionManagerUI.lambda$onUpdatePressed$0(ContributionManagerUI.java:147)
... 1 more
Caused by: java.net.ConnectException: Connection refused: connect
at java.net.TwoStacksPlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at sun.net.NetworkClient.doConnect(NetworkClient.java:175)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:432)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:527)
at sun.net.www.http.HttpClient.(HttpClient.java:211)
at sun.net.www.http.HttpClient.New(HttpClient.java:308)
at sun.net.www.http.HttpClient.New(HttpClient.java:326)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1169)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1148)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:999)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:933)
at cc.arduino.utils.network.FileDownloader.downloadFile(FileDownloader.java:170)
at cc.arduino.utils.network.FileDownloader.download(FileDownloader.java:128)
at cc.arduino.contributions.DownloadableContributionsDownloader.download(DownloadableContributionsDownloader.java:111)
... 5 more
This is red text you asked for.
go to file>prefarence> On url place paste http://downloads.arduino.cc/packages/package_index.json
deligence:
go to file>prefarence> On url place paste http://downloads.arduino.cc/packages/package_index.json
tried this,
it doesn't solve the problem 
hi
I tried updating board manager on another WiFi network and it worked fine. No error was encountered.
But when I connect my PC to Ethernet wire and then try updating it, there is this same error.
So this issue is with My network service provider, how to rectify it.
You should call them and speak to them.
Check if you are behind a proxy. If you are then go to preferences and add your proxy under network. That should solve it. Based on your error, you are unable to connect to the network.
I have the same problem attempting to install the DUE board, tried 2 internet connections (my home wifi and via 4G on my phone). Same problem. Using a Mac too - any advice would be appreciated.
I got hidden firewall turned on, spent 2 days before I understood what's wrong...
antman81 created a new thread:
http://forum.arduino.cc/index.php?topic=560963