Assigning values to repeating subforms using a script

I am using a script to add values to a repeating subform. Below is a simple example. In the real script I would use a loop to do the inserts.

//declare XML structure

String hrxdproot = /process_data/hrxfaform/object/data/xdp/datasets/data/form1";

//assigning repeating subform number

int i = 1;

//assign a value to the first repeating subform

patExecContext.setProcessDataStringValue(hrxdproot + "/Details[" + i +"]/employee_name", "Aditya");

However, the error I get is

"Target exception: org.w3c.dom.DOMException: INVALID_CHARACTER_ERR: An invalid or illegal XML character is specified. "

I also tried to use a SetValue module to perform the same function and got the above error.

/process_data/hrxfaform/object/data/xdp/datasets/data/form1/Details[1]/employee_name = "Aditya"

Finally, I manually merged a sample xml (with 2 instances of the repeating subform) with the pdf and it worked fine. So I don't think there is a problem in the XML.

Can someone please help...

Aditya