Schema not well formed

I keep getting this error message when I check for well formed (error message below)....can someone please tell me why.. below is a portion of my Schema... all tags are properly closed, and sequence is not misplace....I would post whole code here, however the schema file is rather large.

Error - Line 57, 17: org.xml.sax.SAXParseException; lineNumber: 57; columnNumber: 17; s4s-elt-invalid-content.1: The content of '#AnonType_ret' is invalid. Element 'sequence' is invalid, misplaced, or occurs too often.

 <xs:element name="ret">
      <xs:complexType>

        <xs:attribute name="version" type="xs:string" fixed="1.0" />
        <xs:attribute name="date" type="xs:date" use="required" />

        <xs:sequence>
            <xs:element name="feed" type="xs:string" minOccurs="0" maxOccurs="unbounded">
                <xs:complexType>
                    <xs:sequence>