Today, none of my AWS Powershell scripts would work any more. They were all returning
... : Value cannot be null.
Parameter name: awsAccessKeyId
Coincidentally, my Visual Studio would keep on crashing upon startup. I eventually dug into the crash logs and realized that it had to do with the Amazon plugin as well.
Initially I thought it had to do with expired credentials or even the Windows Patch Tuesday.
However, I ended up reinstalling AWS Powershell (and with a much newer version) and the problem went away.