For each PDF/A-1 validation issue we try to explain what it means and, if possible how to resolve it. For a more technical explanation of the issue we quote the related section of the ISO 19005-1 PDF/A Specification.
When the PDF/A file contains LZWDecode compression it is replaced with FlateDecode compression due to intellectual property constraints.
How can I fix it?
Open your PDF file in Solid PDF Tools and then File | Save As PDF/A. This will replace the LZWDecode compression with FlateDecode compression in your PDF/A file.
6.1.10 - ISO 19005-1 PDF/A Specification:
The LZWDecode filter shall not be permitted.
NOTE: The use of the LZW compression algorithm has been subject to intellectual property constraints.