"The 'Microsoft.ACE.OLEDB.12.0' provider is not registered on the local machine."
Guess into the blue: Your Win App is 32 bit and you (may) have installed ACE as 32 bit data provider; that matches on bitness and works.
You ASP.NET app is 64-bit and can't uses 32-bit data provider; that don't work and causes the error.
Install additional ACE as 64 bit or let ASP.NET run as 32-bit app (not prefered).