Trouble validating an xml document

I'm supposed to be writing a DTD for an xml document but there is one particular section that is throwing me for a loop. In the EnrolledIn element there is character data and then course elements. I've tried to validate with the DTD below but I keep getting the error

"ERROR: Element EnrolledIn content does not follow the DTD, expecting (CDATA , Course+), got (CDATA Course Course Course Course )

ERROR: Element EnrolledIn content does not follow the DTD, expecting (CDATA , Course+), got (CDATA Course )".

I've tried using * and + after course but with no success. I'm using Notepad++ xml tools to validate.

<!DOCTYPE Students [
<!ELEMENT Students (Student*)>
<!ELEMENT Student (LastName, MiddleInitial?, FirstName, EnrolledIn?)>
<!ELEMENT LastName (#PCDATA)>
<!ELEMENT FirstName (#PCDATA)>
<!ELEMENT MiddleInitial (#PCDATA)>
<!ELEMENT EnrolledIn (CDATA, Course+)>
<!ELEMENT Course (#PCDATA)>
]>




<Students>
    <Student>
        <LastName> Doe </LastName>
        <MiddleInitial>K.</MiddleInitial>
        <FirstName>John</FirstName>
        <EnrolledIn>
            Courses enrolled in:
            <Course>
                TCSS 445 – Database Systems Design
            </Course>
            <Course>
                TCSS 422 – Operating Systems
            </Course>
            <Course>
                TCSS 422 – Operating Systems
            </Course>
            <Course>
                TBUS 301 Quantitative Analysis for Business
            </Course>
        </EnrolledIn>
    </Student>
    <Student>
        <LastName> Smith </LastName>
        <FirstName>Amy</FirstName>
        <EnrolledIn>
            Courses enrolled in:
            <Course>
                TBUS 100 Introduction to Business
            </Course>
        </EnrolledIn>
    </Student>
    <Student>
        <LastName> Doe </LastName>
        <MiddleInitial> L. </MiddleInitial>
        <FirstName>Jane</FirstName>
    </Student>
</Students>