All main folders 755 and 644 for files... I'm getting crazy

error_log ?
Any errors when you upload the zip file?

error_log ?
Any errors when you upload the zip file?

Hello there,

I would also like to chime in on this, as I seem to be getting the same issue. I updated Joomla to 3.7.5 back on July 31st, and K2 to 2.8 on August 21st.

As the OP mentioned, after any kind of save I receive a blank white screen. After turning on Debugging Information through Joomla's system information, I had received no information or errors. I've checked the console window and there is also no information or errors. However, when I looked at my log files, I noticed several errors about "File does not exist" with it being multiple different files; although I do not think it pertains to this problem.

I tried to reinstall K2 by the zip file from the main website, and the same error persisted.

Can you send some of these errors?

These are the logs that are in my current log files.

[Tue Aug 29 05:15:01 2017] [error] [client xxx] File does not exist: sitehere.com/famvir.org
[Tue Aug 29 06:17:15 2017] [error] [client xxx] File does not exist: sitehere.com/long.Florid
[Tue Aug 29 06:17:45 2017] [error] [client xxx] File does not exist: sitehere.com/Scrub.Com
[Tue Aug 29 06:22:13 2017] [error] [client xxx] File does not exist: sitehere.com/Amilia.Seseka
[Tue Aug 29 06:42:59 2017] [error] [client xxx] File does not exist: sitehere.com/information.Clearl
[Tue Aug 29 06:43:36 2017] [error] [client xxx] File does not exist: sitehere.com/www.securityfocus.com
[Tue Aug 29 07:03:36 2017] [error] [client xxx] File does not exist: sitehere.com/MIA.The

As I've mentioned, I do not believe these logs pertain to K2.

Same problem for me. When I try to save a k2 item, I get a blank page. I see this error in log after trying:

2017-08-30 10:38:24.338 [NOTICE] [xx.x.xxx.xx:63660:HTTP2-25] [STDERR] PHP Fatal error: Cannot redeclare class upload in /home/xxx/domains/xxxxxxxxx.xx/private_html/administrator/components/com_k2/lib/class.upload.php on line 624

@Tyler, these do look suspicious
@Tyler, @neppers, Disable all K2 related extension until you find which one is causing the issue. K2 Multi Images is known to cause a similar issue.

I can confirm that problem goes away when disabling multiimages-plugin. My site depends on this plugin, so it would be very nice to have this solved quickly. If you can find a quick fix, it would be very appreciated.

:-)

I don't use multi-images plugin. No solution for me