I have been able to login to DLS but when i want to download or place it in the cart , I get this message:
" unable to aquire write access to UserData folder."
What is it and why do I get it?
The message is referring to the \userdata folder in your Trainz installation folder. I'd guess you didn't install it as an Admin so the folder is read-only and the game/DLS can't open the folder for insertion of the content.
Register your 2010 and perhaps it will install; probably not until you adjust the privileges for that folder.