Hi in your SPQuery please remove tag, also please escape character to remove empty space in your query.
query.Query =
@"" +
""; query.Query = @"<Where><Or><Membership Type='CurrentUserGroups'><FieldRef Name='Users'/></Membership>" + "<Eq><FieldRef Name='Users'/><Value Type='Integer'><UserID /></Value></Eq></Or></Where>";
you can also limit on results returned to one if you would like to by
query.RowLimit = 1;
If this fails, can you please debug can you please post the query value which you get? This should positively work.