Could not remove the old plugin. Plugin update failed.
This problem about drove me insane on my Windows 2012 R2 server running IIS 8.5 (IIS 8.5.9600.16384 to be exact). It seems like it might be a WordPress windows permission issue, and you’ve likely already seen the recommendations that you add the IUSR, IIS_IUSRS and NETWORK permissions to the folder, or even to check to the folder attributes and make sure read only isn’t on, however in my case this wasn’t the problem. If you are able to restart IIS and then immediately afterwards install the plugins without an issue, you likely have a WinCache problem. Many people have installed WinCache using the Microsoft Web Platform Installer 5.0
and it installs a really old WinCache .dll file! The key to fixing your WordPress 4.x plugin update problem is to download the most recent DLL files and put them in your PHP extensions folder! It took me a while, but I found the most recent Windows DLL files here
! The file name tells you what you need to know wincache-220.127.116.11-dev-5.4-nts-vc9-x86.exe
is for PHP 5.4 nts means non-thread-safe. I installed that file in my C:\Program Files (x86)\PHP\v5.4\ext folder and overwrote the old php_wincache.dll and php_wincache.pdb files. Make sure you backup those files in case something goes awry. I also have PHP 5.5 on the server so I repeated the process and downloaded wincache-18.104.22.168-dev-5.5-nts-vc11-x86.exe
and installed to my C:\Program Files (x86)\PHP\v5.5\ext folder. You’ll need to stop IIS to do this.
I think as a Windows server administrator you always think it’s a permissions issue, but in this case it was a caching issue from an old dll file.
Please Google +1 to help other sysadmin’s find this fix!
Other error messages Plugin could not be deleted due to an error: Could not fully remove the plugin(s) wp-super-cache/wp-cache.php.
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