compilation error while adding web reference RS05

hi,
if i try to add a web reference in my c# application to reporting services
2005 i got a compilation error.
a part of the displayed message:
--
source error:
line 4: <%@. Import Namespace="System.Xml" %> <-- is a red line
error message:
CS0234: The type or namespace name 'Xml' does not exist in the namspace
'System' (are you missing an assembly reference?
do anybody know a solution for this problem?
thx
MartinTake a look at this forum:
http://forums.microsoft.com/msdn/ShowPost.aspx?PostID=10847
particularly the post from AkhilaL MSFT
Jens Konerow