Passing A Value -- HELP!

Greetings!

I'm getting the following error:

Error:         java.lang.NumberFormatException: For input string: "<%cPk%>"
Reason:        For input string: "<%cPk%>"

Basically I aimed to pass a hidden value from one application to another, in order to hide the URL location from users' browsers.

I used a "POST" form instead of a "GET", and used the correct input tag - <input TYPE="hidden" name="cPk" value="<%=cPk%>">

However, I suspect that the value of cPk, a primary key, is not being correctly passed  in the proper format .. although I made the types consistent in my code (and when I hardcoded a number value, I know conceptually this thing should actually work):

Here is the relevant code from the class in the first application:

=========================================================================================
   protected Double cPk;

   public Double getCPk() {
        return cPk;
    }

    public void setCPk(String getCertificateUrl) {
        cPk = new Double(getCertificateUrl);
    }
    public String getCertificateUrl() {
        String cPk = certification.certificationPk().toString();
        //String url = "https://hostname/etc/WebObjects/PDFGenerator.woa/wa/viewReport?cPk=" + cPk;
        //String url = certification.certificationPk().toString();
        return cPk;
    }
========================================================================================
   and here is the relevant code in the second application:

========================================================================================
protected Double cPk;

private NSArray lookupCertification() {      
        // Lookup Certification via cPk
        return fetchSearch("getCertificationPk", "Certification", "cPk", getCPk(), this.session().defaultEditingContext());
    }
   
    public Double getCPk() {
        return cPk;      
    }

    public void setCPk(String newCPk) {
        cPk = new Double(newCPk);
    }
========================================================================================
and here is some more relevant code from another class:
========================================================================================
public void takeFormValues(NSDictionary value) {
        java.util.Enumeration e = getValueList().objectEnumerator();

        while (e.hasMoreElements()) {
            String key = (String)e.nextElement();

            Object obj = context().request().formValueForKey(key);
            if (obj != null) {
                takeValueForKey(obj, key);
            }
        }
    }
========================================================================================

I am ripping what little is left of my hair out ... I suspect the issue is trivial but the cause of the error is beyond me.

Any advice and or guidance would be greatly appreciated!

Best regards,
nearly hairless jamie