Has anyone encountered this before?
I am unsure of the exact cause, but here are the details from the DNN Admin Log:

AbsoluteURL:/DesktopModules/Hotcakes/API/mvc/checkout/CleanCreditCard
DefaultDataProvider:DotNetNuke.Data.SqlDataProvider, DotNetNuke
ExceptionGUID:21b750f8-e01e-4fd6-8e74-f22efbeb2e93
AssemblyVersion:
PortalId:-1
UserId:-1
TabId:-1
RawUrl:
Referrer:
UserAgent:
ExceptionHash:W<<>>k=
Message:Length of the data to decrypt is invalid.
StackTrace:
at System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount)
at System.Security.Cryptography.CryptoStream.FlushFinalBlock()
at System.Security.Cryptography.CryptoStream.Dispose(Boolean disposing)
at System.IO.Stream.Close()
at System.IO.StreamReader.Dispose(Boolean disposing)
at System.IO.TextReader.Dispose()
at Hotcakes.Modules.Core.Controllers.CheckoutController.DecryptStringFromBytes(Byte[] cipherText, Byte[] key, Byte[] iv)
InnerMessage:
InnerStackTrace:
Source:mscorlib
FileName:
FileLineNumber:0
FileColumnNumber:0
Method: