长度不能小于零。参数名称:length”，当使用Sitecore在站点中调用ASPX WebMethod时

I'm receiving "Length cannot be less than zero. Parameter name: length" errors when calling a WebMethod on a plain ASP.NET WebForms (ASPX) page. The error gives no clear idea (that I can see) as to what the problem is, and both GET and POST calls to other WebMethods with similar signatures on the page work.I'm receiving "Length cannot be less than zero.