Here is a response on the Rose Hill Wine Cellars blog (a EuroCave dealer) related to a similar complaint:
Frost at the bottom of the back wall is normal, but a block of ice isn’t…
When you have a case of ice build-up it is generally caused by :
*Bottles touching the back wall and preventing a proper air circulation.
* The unit is ‘breathing’ warm air. You have to eliminate all heat sources around the unit. Close heating vents or heaters, sun hitting the unit directly, warming floors…
* Check the seal of the door by attempting to insert a cardboard business card, if there is no resistance the rubber seal may need replacement.
* Make sure the carbon filter is present, if it is not in place it will leave a hole in the back wall that will let ambient air penetrate.
* Verify the temperature setting, a unit set at 8 in a room that measures 23 will surely condensate a little more than a unit set at 12 in a room that’s 20 degrees. We tend to heat homes in winter warmer than we condition them in the summer, so this is something that can happen this season.
Hope this helps!