原因
估计是昨天连接时，用的本机数据库，使用.作为本机数据源。如：
<add name="StrCon" connectionString="Data Source=.; Initial Catalog=MYPPA; Integrated Security=SSPI;"/>
解决
网上找到解决方法 http://social.msdn.microsoft.com/forums/en-US/sqlgetstarted/thread/17b68347-9e29-4b5c-9358-0f039d4ce0ea/
如下：
QUESTION:
I've installed SQL Server 2005 SP1 RTM on a Windows 2003 R2 machine (machine A), and my local workstation (machine B).
From machine B, I can use SSMS to connect to SQL Server on machine A. This is using either "New Query" or "Object Explorer".
However, on machine A, SSMS can only connect to machines A or B using the "New Query" option. If I try "Object Explorer" for either, I get the error message "Failed to retrieve data for this request... urn could not be resolved at level Configuration."
I'm not sure what died (no pun intended) since the last time this worked. Any thoughts on this?
ANSWER:
The same was happening to me without making changes on my PC or my SQL server environment.
ERROR window:
Connect to Server
Failed to retrieve data for this request. (Microsoft.SqlServer.SmoEnum)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&LinkId=20476
urn could not be resolved at level Configuration. (Microsoft.SqlServer.SmoEnum)
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&LinkId=20476"
RESOLUTION was:
1. Open c:Program FilesMicrosoft SQL Server90dtsBinnMsDtsSrvr.ini.xml
2. Modify the ServerName line to read "(local)" or a more specific server name instead of a "."
3. Restart SQL Server service
SAMPLE:
Code Snippet
<?xml version="1.0" encoding="utf-8"?>
<DtsServiceConfiguration xmlns:xsd="http://www.w3.org/2001/XMLSchemahttp://www.w3.org/2001/XMLSchema">http://www.w3.org/2001/XMLSchema</A< A>>" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
'>http://www.w3.org/2001/XMLSchema-instance">http://www.w3.org/2001/XMLSchema-instance">
; <StopExecutingPackagesOnShutdown>true</StopExecutingPackagesOnShutdown>
<TopLevelFolders>
<Folder xsi:type="SqlServerFolder">
<Name>MSDB</Name>
<ServerName>(local)</ServerName>
</Folder>
<Folder xsi:type="FileSystemFolder">
<Name>File System</Name>
<StorePath>..Packages</StorePath>
</Folder>
</TopLevelFolders>
</DtsServiceConfiguration>
Good luck!
总结
最终还是没按上述方法解决，只是先连接下本地数据库，能打开。然后再连接非本机数据库，就可以了。
网上这个错误好像很少。