You should start from reading this:
http://bugs.ghostscript.com/show_bug.cgi?id=691370
PDF/A-1 standard defines that the architectural limits of PDF 1.4
shall not be violated.
and
The PDF reference (version 1.4 and 1.5 of the reference) limits the
max size of a dictionary to 4095 entries
However:
Given that the dictionary would only be exceeded if required, I'm
doubtful that this would ever happen in practice when producing a
PDF/A file
and
Especially since pdfwrite will only produce dictionaries of the
required size. There is not usually any way to substitute a single
large dictionary with a number of smaller dictionaries, so if we were
to limit the size of dictionaries the only option would be to fail the
conversion with a limitccheck error.
They are talking of pdfwrite.
How are you actually performing the conversion? Which tool?
It it likely that the tool is not following above rule. That may be due to
- the tool is not well designed: change tool;
- the tool has to do so because content can't be converted otherwise: find out which is the part originating the exception.
If you obtain a PDF doc and you can open it, there are tools to analyse its structure in depth. One is http://www.windjack.com/product/pdfcanopener/
Otherwise, Acrobat has Preflight to fix such compatibility errors.