I created and database in sql server 2008. I took the mdf and ldf files to Visual Studio 2010 project and tried to connect to that db with entity-framework. and got the following message:
I cannot reinstall or upgrade the software on the specific computer. So is there any way to downgrade the version of the mdf and ldf files?
No, you cannot downgrade, you will need to move the schema and data another way if you can't install the right version. This recent question is essentially the same:
Essentially you can use the Generate Scripts tool or the Export Data wizard to get your destination database to look like the source. You will not be able attach your MDF file.
And this blog post shows some 3rd party tools that can help with this:
No, you need to install the same or newer version of SqlServer.
There is no known way to downgrade an MDF file.
Perhaps, if you have access to the SqlServer 2008, you could use the command
"Tasks" -> "Create Scripts" to start the wizard to create a script with schema and data.
On the options page there is the button 'Advanced' where you can select the syntax version of SqlServer