I am getting this error message when the JOIN() in ssrs is used.

[rsRuntimeErrorInExpression] The Value expression for the textrun ‘Textbox96.Paragraphs[0].TextRuns[0]’ contains an error: Overload resolution failed because no Public 'Join' can be called with these arguments: 'Public Shared Function Join(SourceArray As String(), [Delimiter As String = ]) As String': Argument matching parameter 'SourceArray' cannot convert from 'String' to 'String()'. 'Public Shared Function Join(SourceArray As System.Object(), [Delimiter As String = ]) As String': Argument matching parameter 'SourceArray' cannot convert from 'String' to 'Object()'.

Any help is appreciated.