Was this problem ever fixed? I'm getting the same error (stack trace below) when I try to save attachments sent via GMail, Yahoo, etc. I have the 5/1/2014 version of ImapX.dll so I'm wondering if the problem was not fixed, or if I might be doing something wrong. My download/save code is the same as the original post above so I'm thinking it might not be me.
at System.Convert.FromBase64_Decode(Char* startInputPtr, Int32 inputLength, Byte* startDestPtr, Int32 destLength)
at System.Convert.FromBase64CharPtr(Char* inputPtr, Int32 inputLength)
at System.Convert.FromBase64CharArray(Char[] inArray, Int32 offset, Int32 length)
at System.Security.Cryptography.FromBase64Transform.TransformBlock(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount, Byte[] outputBuffer, Int32 outputOffset)
at ImapX.EncodingHelpers.Base64.FromBase64(String s) in c:\Users\Pavel\Projects\ImapX\ImapX\EncodingHelpers\Base64.cs:line 107
at ImapX.Attachment.get_FileData() in c:\Users\Pavel\Projects\ImapX\ImapX\Attachment.cs:line 47
at ImapX.Attachment.Save(String folder, String fileName) in c:\Users\Pavel\Projects\ImapX\ImapX\Attachment.cs:line 136
at WindowsApplication1.clsEmailMessages.saveMessageAttachments(Int32 dbID, String[] FileToSaveList, String SaveToFolder, Boolean AutoOverwrite) in C:\Users\Rick\Documents\Visual Studio 2013\Projects\WindowsApplication1\WindowsApplication1\clsEmailMessages.vb:line 170
at WindowsApplication1.SaveAttachments.btnSave_Click(Object sender, EventArgs e) in C:\Users\Rick\Documents\Visual Studio 2013\Projects\WindowsApplication1\WindowsApplication1\SaveAttachments.vb:line 67