Invalid handle to file/path at runtime

Hello:

I have an Android App that uses "Directory.CreateDirectory", "File.WriteAllText" and "FileStream" (test in several ways), and I hava random "Invalid handle to file" or "Invalid handle to path" exceptions.

I use different threads to work. Can be related to the UI Thread? File Access must be on UI Thread to work?

It's not a security or AndroidManifest error, it Works sometimes!

Thanks for your time!