HttpPostedFile.SaveAs() throws UnauthorizedAccessException even though the file is saved

I have an aspx page with multiple FileUpload controls and one Upload button. In the click handler I save the files like this:

string path = "...";
for (int i = 0; i < Request.Files.Count - 1; i++)
{
    HttpPostedFile file = Request.Files[i];
    string fileName = Path.GetFileName(file.FileName);
    string saveAsPath = Path.Combine(path, fileName);
    file.SaveAs(saveAsPath);
}

When file.SaveAs() is called, it throws:

System.Web.HttpUnhandledException:
Exception of type
'System.Web.HttpUnhandledException'
was thrown. —>
System.UnauthorizedAccessException:
Access to the path
'…'
is denied. at
System.IO.__Error.WinIOError(Int32
errorCode, String maybeFullPath) at
System.IO.FileStream.Init(String path,
FileMode mode, FileAccess access,
Int32 rights, Boolean useRights,
FileShare share, Int32 bufferSize,
FileOptions options,
SECURITY_ATTRIBUTES secAttrs, String
msgPath, Boolean bFromProxy) at
System.IO.FileStream..ctor(String
path, FileMode mode, FileAccess
access, FileShare share, Int32
bufferSize, FileOptions options,
String msgPath, Boolean bFromProxy)
at System.IO.FileStream..ctor(String
path, FileMode mode) at
System.Web.HttpPostedFile.SaveAs(String
filename) at
Belden.Web.Intranet.Iso.Complaints.AttachmentUploader.btnUpload_Click(Object
sender, EventArgs e) at
System.Web.UI.WebControls.Button.OnClick(EventArgs
e) at
System.Web.UI.WebControls.Button.RaisePostBackEvent(String
eventArgument) at
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler
sourceControl, String eventArgument)
at
System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean
includeStagesAfterAsyncPoint) —
End of inner exception stack trace —
at
System.Web.UI.Page.HandleError(Exception
e) at
System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean
includeStagesAfterAsyncPoint) at
System.Web.UI.Page.ProcessRequest(Boolean
includeStagesBeforeAsyncPoint, Boolean
includeStagesAfterAsyncPoint) at
System.Web.UI.Page.ProcessRequest()
at
System.Web.UI.Page.ProcessRequest(HttpContext
context) at
ASP.departments_iso_complaints_uploadfiles_aspx.ProcessRequest(HttpContext
context) at
System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at
System.Web.HttpApplication.ExecuteStep(IExecutionStep
step, Boolean& completedSynchronously)

Now here's the fun part. The file is saved correctly! So why is it throwing this exception?

Update

I fixed it by checking for a non zero ContentLength:

string path = "...";
for (int i = 0; i < Request.Files.Count - 1; i++)
{
    HttpPostedFile file = Request.Files[i];
    if (file.ContentLength == 0)
    {
        continue;
    }

    string fileName = Path.GetFileName(file.FileName);
    string saveAsPath = Path.Combine(path, fileName);
    file.SaveAs(saveAsPath);
}