Thumbnail generator not restricting to non-image files

Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Exception:

Source Error: Page_Load

Source File:

Stack Trace:
at Mako.Web.DesktopModules.Blogs.CreateThumbNail.Page_Load(Object sender, EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
Request Parameters:
Image: /Documents and Settings/4/User Documents/2/My Documents/Have You Googled Today.mp3

Size: 150

ASP.NET_SessionId: p0mqbykbsjspbq5zyl22pulf

ALL_HTTP: HTTP_CONNECTION:Close
HTTP_ACCEPT:text/html, text/plain, text/text, text/javascript, text/x-javascript, text/js, text/x-js, text/jscript, text/ecmascript, text/xml, xml/xml, image/, audio/, video/, application/
HTTP_ACCEPT_ENCODING:gzip, deflate
HTTP_FROM:msnbot(at)microsoft.com
HTTP_HOST:www.neoreef.com
HTTP_USER_AGENT:msnbot-media/1.1 (+http://search.msn.com/msnbot.htm)

ALL_RAW: Connection: Close
Accept: text/html, text/plain, text/text, text/javascript, text/x-javascript, text/js, text/x-js, text/jscript, text/ecmascript, text/xml, xml/xml, image/, audio/, video/, application/
Accept-Encoding: gzip, deflate
From: msnbot(at)microsoft.com
Host: www.neoreef.com
User-Agent: msnbot-media/1.1 (+http://search.msn.com/msnbot.htm)

APPL_MD_PATH: /LM/W3SVC/4/ROOT

APPL_PHYSICAL_PATH: E:\inetpub\nodes\OneNet 02\wwwroot\

AUTH_TYPE:

AUTH_USER:

AUTH_PASSWORD:

LOGON_USER:

REMOTE_USER:

CERT_COOKIE:

CERT_FLAGS:

CERT_ISSUER:

CERT_KEYSIZE:

CERT_SECRETKEYSIZE:

CERT_SERIALNUMBER:

CERT_SERVER_ISSUER:

CERT_SERVER_SUBJECT:

CERT_SUBJECT:

CONTENT_LENGTH: 0

CONTENT_TYPE:

GATEWAY_INTERFACE: CGI/1.1

HTTPS: off

HTTPS_KEYSIZE:

HTTPS_SECRETKEYSIZE:

HTTPS_SERVER_ISSUER:

HTTPS_SERVER_SUBJECT:

INSTANCE_ID: 4

INSTANCE_META_PATH: /LM/W3SVC/4

LOCAL_ADDR: 209.210.60.68

PATH_INFO:

PATH_TRANSLATED:

QUERY_STRING:

REMOTE_ADDR: 65.55.211.180

REMOTE_HOST: 65.55.211.180

REMOTE_PORT: 59923

REQUEST_METHOD: GET

SCRIPT_NAME:

SERVER_NAME: www.neoreef.com

SERVER_PORT: 80

SERVER_PORT_SECURE: 0

SERVER_PROTOCOL: HTTP/1.1

SERVER_SOFTWARE: Microsoft-IIS/7.5

URL:

HTTP_CONNECTION: Close

HTTP_ACCEPT: text/html, text/plain, text/text, text/javascript, text/x-javascript, text/js, text/x-js, text/jscript, text/ecmascript, text/xml, xml/xml, image/, audio/, video/, application/

HTTP_ACCEPT_ENCODING: gzip, deflate

HTTP_FROM: msnbot(at)microsoft.com

HTTP_HOST: www.neoreef.com

HTTP_USER_AGENT: msnbot-media/1.1 (+http://search.msn.com/msnbot.htm)