November 2017 update: Martin wrote in below to share that this worked for 10.12 as well.
I have a Lexar Professional ExpressCard Compact Flash Reader, model number LRWEXPP-7000.
Lexar’s latest drivers do not work for MacOS 10.10 and 10.11 because they way they must be installed has changed.
The drivers that Lexar uses are old and out of date and will not install on 10.10 and 10.11 because Apple now requires that all kernel extensions have a proper developer signature. Lexar’s response about that is:
“Thank you for contacting Lexar. Unfortunately, we have no plans on releasing an update for that reader since things have been leaning more towards Thunderbolt series and USB 3.0. I apologize for the inconvenience but you can check out our newer readers”
But I don’t take “No” for an answer and didn’t give up I figured out that Lexar’s reader uses an ATA bridge and drivers made by JMicron. I tried there but didn’t find anything to download on their site. Then I really wished that I had bought the Sonnet Technologies “Pro Dual Compact Flash ExpressCard/34 adapter” instead. I saw one for auction and was going to bit, but I figured that I should try to see if their software would install before I try to get the Sonnet ExpressCard.
I went to Sonnet Technologies’ website and download the driver for the “Pro Dual Compact Flash ExpressCard/34 adapter” (the 1.0.6 version I downloaded was released Nov 2014) and tried to install it. It succeeded in installing, which was good, but suddenly my Lexar Professional Express Card Compact Flash Reader’s activity light started blinking and my CF mounted on my MacBook Pro’s desktop that is running El Capitan.
The Sonnet driver tries to first install the JMicron driver and fails but then goes on to install CFRW2X-E34.kext instead and it works for my Lexar ExpressCard! It’s also got a nice Finder icon of a CF card instead of the generic orange one and in the System Information (Profiler) it properly identifies what brand type of card is installed.
Hope that is helpful for Mac users out there. In this case persistence paid off and I now can continue to use this reader for the foreseeable future.
I’m super happy now.
Use at your own risk, but I can confirm that this works just fine for me. Thanks, Andrew!
PS. If you’re reading this, this probably just saved you a whole bunch of money, so please consider donating a few bucks to a charity like Friends of San Francisco Animal Care & Control. They do truly amazing work.