It seems that Amazon is discontinuing access to their Cloud Drive API. If it is true it means NetDrive will not be able to read or write files from Amazon Cloud Drive. We searched on web and we found that it also affects another softwares like BoxCryptor and Duplicati. Of course you can continue to access your files using web browsers.
One thing we cannot understand is that we have not received any prior notice from Amazon. We sent an email and waiting for their reply.
Sorry for the inconvenience it may caused.