[quote user="Joerg"]The error message itself is OK in case Pmail / IER detects a wrong file format. But why it appears so often?[/quote]
Here we go again, Joerg: Since you describe this error message twice as occuring while replying it can't be an IER error message, and I'm 100% sure it's a TER/HTS error message since I've seen such error messages before. There are further indicators confirming this: IER's own error messages would usually come with a caption showing IER's name and version number as their title - if they don't come as an exception dialog which usually includes the exception code and address. Errors only affecting replies, forwards or printing are usually TER/HTS errors, only so-called runtime errors and exceptions might come from other modules except when clearly indicated as IER error messages as explained above.
Now with regard to fixing such an error: No chance except for buying a more recent TER/HTS version by David Harris as discussed in a recent thread. I do already fix such errors by decoding and recoding faulty PNG files when they come as embedded images within the HTML message (it's possible to do this), but if they come as attached parts in a multipart/related MIME message the images aren't submitted to the HTML renderers for fixing prior to Pegasus Mail's reply, forward or print processing with TER/HTS.
Sorry to say (and not to know why this dialog shows up more than once) ...
Michael -- PGP Key ID (RSA 2048): 0xC45D831B IERenderer's Home: https://www.pmpgp.de/renderer/History.htm S/MIME Fingerprint: 94C6B471 0C623088 A5B27701 742B8666 3B7E657C