Invalid length for a Base-64 char array or string

Posted by: phil on 14 December 2018, 2:44 am EST

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    Posted 14 December 2018, 2:44 am EST - Updated 30 September 2022, 12:00 am EST


    Im using the richtextbox for silverlight component. On the odd email I’m getting an error when I set the html property of the component to the contents of the email:

    System.FormatException: Invalid length for a Base-64 char array or string

    Any ideas as to the cause? I’ve attached a longer version of the error so you can see where it’s coming from.



  • Posted 16 December 2018, 11:50 pm EST

    Hello Phil,

    Thank you for attaching the stack trace of the exception.

    The probable cause of the exception might be that your mail content is having some “spaces” and “+” which are creating issues.

    So,could you please confirm the following:

    1. Whether/not you are using the latest version of ComponentOne at your end.
    2. Check whether the exception comes with every email content/not. If it is related to a specific email only, please share the odd email content for us to check. If you have any issues sharing the contents here, please share the same at



  • Posted 17 December 2018, 4:07 am EST


    thanks for the reply.

    I’ve narrowed down the issue. In trying to create a test email for you, I’ve discovered that it’s to do with images, specifically when there’s a base64 encoded image that’s invalid.

    In fact no base64 encoded images display.

    • Valid ones do not display, which is no problem for us.
    • Invalid ones though cause an error which is a problem.

    I’ll write some code to strip out all base64 encoded images and that’ll solve the problem.

    Finally to answer your question on versions we are a bit out of date, so perhaps you’ve fixed this is a more recent update.



  • Posted 17 December 2018, 10:36 pm EST

    We are glad to know you have found the issue and have successfully resolved it.

    Let me know, if you need any help.


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