Dymo LabelWriter 400. How do I leave a blank line space? When I print the label it reverts to single spacing and not the double.

Older Dymo labeler and not supported. It says to contact them. The software for Windows only went as far as Windows XP. Time for you to upgrade.

https://www.dymo.com/en_CA/online-support-compatibility-chart

LabelWriter 300 and 400 Series Print Drivers Windows ... - Dymo

https://www.dymo.com > en_CA > dymo-labelwriter-300-...
Please enter model number. Select Product Model. Please enter model number. Find downloads. Close. Can't Install Your LabelWriter 450/450 Turbo?

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  Downloads: Software, Drivers & User Guides - Dymo

  https://www.dymo.com > online-support-user-guides
  The Latest Software & Drivers for all LabelWriters® and LabelManagers®. Supports all LabelWriter® 5 series, 450 series, 4XL, and LabelManager® 280, ...
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  Compatibility-Chart ' DYMO

  https://www.dymo.com > online-support-compatibility-chart
  DYMO Connect for Desktop 1.4.2- the latest DYMO software for Windows® operating system ... LabelWriter® 450 Twin Turbo ... LabelWriter® 400 Turbo

When you type the label just press return or enter and it will skip a line. Hope this helps.

Double check that your using correct printer driver.
Completely remove restart computer with printer discontente,then reinstall the printer.

It may be that it is only out of ink

https://dymo.custhelp.com/app/answers/detail/a_id/1343/~/failed-to-convert-devmode-to-print-ticket-error-when-printing-from-dymo-label

These Dymo LabelWriters are thermal printers which uses heat to print the labels, not ink. Be sure you are using labels compatible with your Dymo printer.

http://global.dymo.com/enGB/Troubleshooting/LabelWriter_320.html

From this site.

• • The error message: "Exception Eprinter in module LABELS.DLL at ...." is displayed.
    or
    The error message: "Access violation at address ... in module DYMOLBL.EXE" is displayedA. This problem can occur when DLS 7.x was installed over DLS 6.x, without first uninstalling DLS 6.x.
    Solution:
    Delete the file Dymolbl.ENG.
    DLS will still work, however, all default settings will be incorrect.
    
    The settings will need to be set correctly.
    On the DLS menubar, click Preferences and set the preferences as desired.
    The default values are:
    Default label file folder should be set to "C:\Documents and Settings\All Users\Shared Documents\DYMO Label\Label Files"
    Default address book folder should be set to "C:\Documents and Settings\All Users\Shared Documents\DYMO Label\Address Books"
    Default clipart folder should be set to "C:\Documents and Settings\All Users\Shared Documents\DYMO Label\Clipart"
    
    B. An incorrect printer has been selected in the DYMO software.
    Solution:
    1. Start the DYMO Software.
    2. Click on File and point to Change printer.
    3. Click the LabelWriter model connected to the PC (e.g. Dymo Turbo)
    
    
    C. Occasionally, double-clicking the print command button in the list manager is not handled properly by the software.
    Solution:
    Single-click the print command button.
    
    
    D. An incorrect driver has been installed.
    Solution:
    Run the DYMO Driver Uninstaller
    Restart the PC and install the correct driver.
    
    To remove and reinstall the printer driver:
    1. On the Windows taskbar, click Start, point to Settings and click Printers (& Faxes).
    The printers window is displayed.
    2. Double-click the LabelWriter icon and delete any documents waiting to be printed.
    3. Close all programs.
    4. On the Windows taskbar, right-click on Start and click Explore.
    Windows Explorer is started.
    5. Double-click the file C:/Program Files/DYMO Label/Support Files/LW Remove.exe
    6. Unplug the LabelWriter's USB connection from the back of pc and click OK.
    7. Choose Select all and then remove.
    Once the driver has disappeared from the printers dialog box, click Close.
    Restart the PC.
    8. When Windows has restarted, on the Windows taskbar, click Start, point to Programs, point to DYMO Label and click Uninstall DYMO Label.
    9. Reconnect the LabelWriter to the computer and reinstall both driver and software.
    

It could be how you have loaded the labels. If you have loaded the labels and there is a small gap between the spindle and the roll, it will print one label and give a error-printer message and stop working until you unplug it for 30 seconds and plug it back in. I would reload the labels from scratch and ensure there is no gap.

Did you change the number of copies to print prior to printing?