Converting a lead via crm api with javascript

I have been trying to convert a lead via the api.

This is the error I get:

<response uri="/crm/private/xml/Leads/convertLead"><error><code>4600</code><message>Unable to process your request. Please verify whether you have entered proper method name,parameter and parameter values.</message></error></response>

This is the url I am sending:

https://crm.zoho.com/crm/private/xml/Leads/convertLead?authtoken=********************************&scope=crmapi&leadid=971240000007521007&xmlData=%3CPotentials%3E%3Crow%20no=%221%22%3E%3Coption%20val=%22createPotential%22%3Efalse%3C/option%3E%3Coption%20val=%22assignTo%22%3Edcrowell@roofscope.com%3C/option%3E%3Coption%20val=%22notifyLeadOwner%22%3Etrue%3C/option%3E%3Coption%20val=%22notifyNewEntityOwner%22%3Etrue%3C/option%3E%3C/row%3E%3Crow%20no=%222%22%3E%3CFL%20val=%22Potential%20Name%22%3ESamplepotential%3C/FL%3E%3CFL%20val=%22Closing%20Date%22%3E12/21/2009%3C/FL%3E%3CFL%20val=%22Potential%20Stage%22%3EClosed%20Won%3C/FL%3E%3CFL%20val=%22Contact%20Role%22%3EPurchasing%3C/FL%3E%3CFL%20val=%22Amount%22%3E3432.23%3C/FL%3E%3CFL%20val=%22Probability%22%3E100%3C/FL%3C/row%3E%3C/Potentials%3E

I am sending this via javascript request. What am I doing wrong?

Thanks in advance for any help.