Due:
Our attachment control inside, the size of the default settings in general as 10M, 30M if we set up the situation, we can not meet uploaded.
the reason:
Because a file ajax's take our custom-sized control value we can not get to. Because we pass an int, so when we take a QueryString value Null.
solve:
Open Portal-> Ajax-> FileUploadHandler.ashx file, locate the following code:
ProtectedintMaxSize
{
get
{
if(!int.TryParse(Request.QueryString["MaxSize"],Out _maxSize))
{
_maxSize = 10 * 2014;
}
return_maxSize;
}
}
We put the corresponding Request judging portion into the following code:
Request.Params["MaxSize"]
You can implement a custom attachment upload control properties.
Figure shows the effect: 
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