If you want to allow a filetype like e.g. *.mdb it's not enough to allow that type within SharePoint.
You've to allow it as well within IIS (if request filtering is enabled)
That can be done manually
OR: if you've multiple IIS Servers within your SharePoint Farm via PowerShell Script:
$servers = "server1","server2","server3","server4"
foreach ($server in $servers)
{
Invoke-Command -computername $server -ScriptBlock {
import-module webadministration
Function Enable-IISFileExtension
{
PARAM(
$ConfigFile,
$FileType,
$Flag
)
$xml = [XML](Get-Content -Path $ConfigFile -ErrorAction STOP)
$item = $xml.configuration."system.webServer".security.requestFiltering.fileExtensions.add | Where-Object {$_.fileExtension -match "$FileType"}
$item.allowed = $Flag
$xml.Save($ConfigFile)
return $xml.configuration."system.webServer".security.requestFiltering.fileExtensions.add | Where-Object {$_.fileExtension -match "$FileType"}
}
Enable-IISFileExtension -ConfigFile "C:\Windows\System32\inetsrv\config\applicationHost.config" -FileType ".mdb" -Flag "True"
Exit-PSSession
}
}