Common problems and resolutions

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General software problems

When I try to start the software, I get a Java error.

Nxt relies on Java 8.  Make sure you download and install latest version installed from Oracle! You can check to see which version of Java is running on your computer by running the following command in a terminal window:

java -version

I get "java.lang.NullPointerException" when trying to open http://localhost:7876/ or

If your Java version is already up to date, this may indicate your blockchain data has been corrupted. Often stopping and restarting your server is all it takes to resolve this condition. See also "My blockchain files keep getting corrupted".

When I access my server, I get a black screen and the words "The matrix has you". What is happening?

If you are running Nxt on your local computer AND are accessing it by browsing to (or http://localhost:7876/), you should not get this error. But it will likely appear if you have installed Nxt on a public server, VPS and are trying to access it remotely. For security reasons, the software is distributed under the assumption that the only way you access Nxt is from your local computer. This is the most secure way to use Nxt. If you want to be able to access and log in to your client from elsewhere, and have not edited the configuration files to allow this, you will get the "matrix" message. To remove this, you need to create or edit a configuration file. Under your nxt folder, you will find a conf directory. Inside that directory, create a file called, if it does not already exist, and add this line to the file:

nxt.allowedUserHosts=[YOUR IP ADDRESS]

...where [YOUR IP ADDRESS] is the IP address or hostname from which you'd like to be able to connect. If you are not concerned about security, you can enter * here. Be warned that this means that your server will accept logins from anyone... including hackers and attackers.

I cannot load the client in a web browser

First of all, you need to make sure that the Nxt server window has finished loading, as indicated by a message like this:

Nxt Server 1.12.2 started successfully.

To access your client interface, you can then use either of these addresses:


My blockchain won't load!

Patience is usually the best fix; your client will eventually catch up with the network. Some delay may occur specially when you have updated to a new software version that performs a database upgrade.

My blockchain files keep getting corrupted

The blockchain database may get corrupted as a result of the Nxt software being forcefully terminated, in a way that doesn't allow the server to close the database properly. You should be able to see "Database shutdown completed" in the log before shutdown, as a sign that data files have been properly closed. To prevent data corruption when closing Nxt:

  • In Windows, use Ctrl-C to shut down the process in the terminal window
  • In UNIX, use kill -15 #ID PROCESS. (Jean-Luc)

MacOS-specific software problems

I'm running MacOS 10.6, and it won't support Java 1.7. Do I have to update MacOS?

No! There is a workaround for installing Java JDK 1.7 on MacOS 10.6. You must be comfortable editing plist files in order to use this workaround.

  1. Go to:
    • /System/Library/CoreServices
  2. Edit:
    • SystemVersion.plist
  3. Change: ProductUserVisibleVersion = 10.6.x and ProductVersion = 10.6.x to:
    • ProductUserVisibleVersion = 10.7.8
    • ProductVersion = 10.7.8
  4. Install JDK 7 and change SystemVersion.plist back to normal
  5. Go to and open /Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk
  6. Uncheck both Java 6 VMs. Now Java 7 will load first.

Account problems

The client says I have 0 NXT in my account but I have not transferred my coins anywhere

In some cases, right after unlocking your account in the client, the balance might momentarily appear like zero or a different amount than expected. This will happen if the blockchain has not been completely downloaded by your software yet, and the blocks containing your deposits are yet to be downloaded. Check the time stamp on the latest block in the "Blocks" panel. If it is not very recent (within a minute or two), wait and give the software some time to catch up. Your balance should match the balance showing for your account in the blockchain explorer in a few minutes.

I'm trying to unlock my account, but I keep accessing a different account number than the one I created. What's going on?

Since different account numbers are accessed using different passphrases, getting a different account number than the one you expected means you used a different passphrase than the one originally used to generate your account number. Make sure you are introducing your original passphrase correctly. This means double-checking for typing mistakes, and ensuring no extra spaces are accidentally pasted (or omitted!) in the beginning or the end of your passphrase as you paste it to unlock your account.

I created an account but I don't see it referenced in the blockchain

In general, you can use the blockchain explorer to search for your account, examine your balance, transaction history, and more.  Information about your account will not appear in the blockchain until there is at least one confirmed transaction that references your account.  This is because the blockchain is a record of transactions, not account information. If you have created an account but have never sent any Nxt to it, the account will not appear in the blockchain. From here, you may want to learn more about the Nxt client or read our Faq!