ASM BufferOverflow on pdf File upload

I dont want to disable this signature completely and i want to understand why it is happening. Below are the request headers for the one which is not getting uploaded -

POST /japanvoice.aspx HTTP/1.1 Accept: text/html, application/xhtml+xml, image/jxr, / Referer: https://ejalgaon.india.com/japanvoice.aspx Accept-Language: en-US User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; Touch; rv:11.0) like Gecko Content-Type: multipart/form-data; boundary=---------------------------7e2692020986 Host: ejalgaon.india.com Content-Length: 52078 Connection: Keep-Alive Cache-Control: no-cache Cookie: ASP.NET_SessionId=0odrduerk2bh3l40ge2nvojb;