The issue can be due to the limit of httpRuntime default maxRequestLenght which if 5MB, but this is genarlly caused if you try to upload the files to server having size more than 5MB.
try the same after adding the below line to the web config. might that help
<httpRuntime maxRequestLength="1048576" executionTimeout="360"/>
or the issue can be cause by the iis. Read more about maxAllowedContentLength.
also check the link