On manufacturer's website I found following statement regarding the data format:
Extended Gerber
Layer 1
Excellon format 2,5 inch or 3,3 mm
Supress Leading Zero
(Don’t forget to include the drill sizes.)
Layers 2-7 - Gerber 274x
In DesignSpark there is no supress leading zero feature. I contacted the manufacturer and sent them extended gerber files from DesignSpark. They will accept this. So it is not a problem in my case. If anyone has a problem with this, you can post it here.