Concat Function throws XPath Exception : Value does not match required type

@Line

Hello,

I am using Oracle BI Publisher 11.1.1.7.0 and the follow expression is throwing an exception during report generation.

<?concat(CCity,', ',CSt,' ',CPostal)?>

After looking at the log this is what I found

[111017_110831791][oracle.xdo.common.xml.XSLTWrapper][ERROR] XSL error:

<Line 46, Column 193>: XML-23006: (Error) value does not match required type

@Line 46 ==> </_A><_B><xsl:value-of select="concat(/query/row/CCity, ', ', /query/row/CSt, ' ', /query/row/CPostal)" xdofo:field-name="concat(CCity,', ',CSt,' ',CPostal)"/>

I dont see any syntactical errors and was curious if anyone else had run into this problem. I have attached the RTF and XML files.