How to solve this problem I have with a restore (backup) file I made in SQL Server 2008?

I have made a time ago a file backup in SQL Server 2005. Now, I am using SQL Server 2008. I made a restore to that file and everything went fine. But, every time I’m trying to add a new table to my DB I get this message I can’t understand why:

“Saving changes is not permitted. The changes you have made require the following table to be dropped and re-created. You have either made changes to a table that can’t be re-created or enabled the option Prevent saving changes that require the table to be re-created”

and I get in list only the new table I just added.

I don’t know what this means at all. I only added one table, no primary key, no connections, nothing else and it refuses to make the change and save it, so now I’m stuck and can’t change anything on my DB.

How can it be?
What may be the problem?
Please help and advise :-(