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I have a problem. When I start pdfLatex using the package media9, there comes this error:

The required file tex\latex\l3experimental\l3str\l3regex.sty is missing.

So, I have downloaded the package l3experimental, but there is no path like this: l3experimental\l3str\l3regex.sty and l3regex.sty doesn't exist (only l3regex.dtx).

So, I have adjusted accordingly the path and renamed the file format into sty, but the error doesn't disappear.

Can You help me, please?

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Welcome to TeX.SX! What operating system and TeX distribution are you using? –  egreg Jan 21 '14 at 17:07
I use miktex on windows 7, 64 bit –  Jack Jan 21 '14 at 17:14
@egreg: Backslashes in the given paths reveal Win as underlying OS. Maybe some outdated MiKTeX is running on it. –  AlexG Jan 21 '14 at 17:15
@Jack Update to MiKTeX 2.9, if you haven't, and use its package manager for updating packages. Don't install them by hand. –  egreg Jan 21 '14 at 17:19
Updating MiKTeX should also include an update (synchronize) of the package data base. See: tex.stackexchange.com/a/107528 –  AlexG Jan 21 '14 at 17:24

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