I am sure, if you are a beginner for Mirth – this screen would have made you to cry. You wont get the text box to enter the Username and Password to login to Mirth Connect.

When it happened for me for the first time, I followed few guidelines over the web; but still could not be recovered. Since I was in hurry and I had a back up of all my mirth channels, hence I went for a fresh installation. But again after few days – the same screen has appeared.
This time I was not into a position to do a re-installation. So here is the proper and perfect solution to get rid off this:

1. Windows 7 and onward system, go to start and in search type – “Java Control“. Click the Java which falls under Control Panel.
The same will appear as Start->Control Panel -> Java
2. After click – now go to General -> Settings -> Delete File
At the same time you can make a larger space for your temporary file by editing the values.

After delete, go to your Mirth Connect Administrator – it should bring up the user name and password screen into a right format.

If you have more channels and processing are of high volumes,
In Mirth Connect 3.3.x
right click on Mirth icon at your system tray -> Show Manager -> Under Server Tab – Server Memory -> Put a higher value now.

In Mirth Connect 3.4.x
right click on Mirth icon at your system tray -> Show Manager -> At the last row of the screen beside “Administrator” there is a “setting/tool” icon
Change the Max Heap Size

But the best would be to change directly from the Mirth configuration file:

C:\Program Files\Mirth Connect\conf\mirth.properties ( or a similar path)

Look for administrator.maxheapsize = <?>
This should fix the problem for some more days – but ultimately you must be cleaning the Java temp file on a regular basis. I don’t want to consume the entire memory to heap, hence I will set an optimal value – never mean I can put a 3 or 4 GB to it.