Sharepoint Caml query special characters

Hi,

I am currently working on a Sharepoint-project where they used some german special chars ('Ä', 'Ü', 'Ö', ...) for their column names. When i query such a column using Caml i allways get an exception similar to this one:

A first chance exception of type 'Microsoft.SharePoint.Client.ServerException' occurred in Microsoft.SharePoint.Client.Runtime.dll.

  The thread 0x1048 ended with Code 259 (0x103).
     at Microsoft.SharePoint.Client.ClientRequest.ProcessResponseStream(Stream responseStream)
     at Microsoft.SharePoint.Client.ClientRequest.ProcessResponse()
     at Microsoft.SharePoint.Client.ClientRequest.ExecuteQueryToServer(ChunkStringBuilder sb)
     at Microsoft.SharePoint.Client.ClientRequest.ExecuteQuery()
     at Microsoft.SharePoint.Client.ClientRuntimeContext.ExecuteQuery()
     at Microsoft.SharePoint.Client.ClientContext.ExecuteQuery()
     at Sharepoint_Test_Engine.SPAction.Trigger(Int32 _itemId) in c:\......\SPAction.cs:Row 73.

How can I encode these special characters? Or are there any other ways to work around this issue?

Thank you in advance.