PDF inclusion: found PDF version <1.5>, but at most version <1. 4> allowed

How do I get rid of this error:

PDF inclusion: found PDF version <1.5>, but at most version <1. 4> allowed


I tried putting \pdfoptionpdfminorversion=5 after my preamble, but nothing happens.

I've seen this error in the following situation.

1. I created some PDFs using TeXLive2010 with the most recent stable PGF/TikZ (in case it is relevant).
2. I cropped these PDFs using pdfcrop, again from TeXLive 2010.
3. I sent these to another person, who included them in their document with the graphicx package.
4. That person used TeXLive 2009 to compile the document.

(I'll need a little time to dig out a MWE! I'll need to figure out how to switch between TL2010 and TL2009 on my machine.)

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 Are you including any other PDFs as pictures? Check the PDF version of them. Which version of pdflatex are you using? – Martin Scharrer♦ Feb 22 '11 at 9:37 I have two pdfs as pictures, how can I find out what version of pdflatex I'm using? – user3749 Feb 22 '11 at 9:45 Both the PDFs are 1.5 – user3749 Feb 22 '11 at 9:47 It is in the first line of the log file. Also check the PDF version of the resulting PDF. – Martin Scharrer♦ Feb 22 '11 at 9:49 Where's the $log$ file? Sorry, I'm new at this :S – user3749 Feb 22 '11 at 9:55
Did you try \pdfminorversion=X ? At least it works for me...