New Post: System.Xml.XmlException: The ';' character, hexadecimal value 0x3B, cannot be included in a name

As the title says, I get the error message in the Composite console and do not know where to start looking.

I have found some similar threads, but talk about older versions one 4.1
https://compositec1.codeplex.com/discussions/281056
https://compositec1.codeplex.com/discussions/468228

Build I use:
Composite C1 4.1
Build no. 4.1.5058.34326

Does anyone have an idea about the error

__Critical AdministrativeOutputTransformationHttpModule  __
System.Xml.XmlException: The ';' character, hexadecimal value 0x3B, cannot be included in a name. Line 6, position 659.
at System.Xml.XmlTextReaderImpl.Throw(Exception e)
at System.Xml.XmlTextReaderImpl.ParseElement()
at System.Xml.XmlTextReaderImpl.ParseElementContent()
at System.Xml.XPath.XPathDocument.LoadFromReader(XmlReader reader, XmlSpace space)
at System.Xml.Xsl.Runtime.XmlQueryContext.ConstructDocument(Object dataSource, String uriRelative, Uri uriResolved)
at System.Xml.Xsl.Runtime.XmlQueryContext..ctor(XmlQueryRuntime runtime, Object defaultDataSource, XmlResolver dataSources, XsltArgumentList argList, WhitespaceRuleLookup wsRules)
at System.Xml.Xsl.Runtime.XmlQueryRuntime..ctor(XmlQueryStaticData data, Object defaultDataSource, XmlResolver dataSources, XsltArgumentList argList, XmlSequenceWriter seqWrt)
at System.Xml.Xsl.XmlILCommand.Execute(Object defaultDocument, XmlResolver dataSources, XsltArgumentList argumentList, XmlSequenceWriter results)
at System.Xml.Xsl.XmlILCommand.Execute(Object defaultDocument, XmlResolver dataSources, XsltArgumentList argumentList, XmlWriter writer)
at System.Xml.Xsl.XslCompiledTransform.Transform(XmlReader input, XsltArgumentList arguments, XmlWriter results)
at Composite.Core.WebClient.Presentation.OutputTransformationManager.XslTransformationStream.Transform(MemoryStream buffer, String mode, String browser, String platform)
at Composite.Core.WebClient.Presentation.OutputTransformationManager.XslTransformationStream.Close()