How to change the idSeperator in any char you want. The IdSeparator is the char, that splits 2 id's in NamingContainers. per default the char is the '$' (dollar) and you'll see it in every id, name and so on in the source code of your Page. like ctl00$HolderContent$Login1$pnlForm. so it should be something, that you don't use in your control Id's.