How to deal with QNap error "your login credentials are incorrect or your account is no longer valid" while signing in to web interface

 In this article I explain how to solve the problem while signing in to web interface of Qnap.

I did a research in the web before I successfully solved the problem. You can find many topics like this on internet forums, but most of them were not solved and no one could be able to answer this case completely. What's strange, you're trying to sign in to web interface of your qnap in web browser and the login and password are wrong, but using the same credentials via ssh command is successfull. So, it gave me a hint that something may be wrong with the web interface.

First, you can sign in to ssh of your Qnap and execute following command:

cd /etc/init.d

./Qthttpd.sh restart

./thttpd.sh restart

then refresh the login page (e.g. http://192.168.0.114/cgi-bin/) in your browser. Try to login via web interface. If it's not succeed, please read further.

Second method is based on the assumption, that there is a lack of ram memory in your Qnap. Execute following command in bash:

$ df -hT /
Filesystem           Type            Size      Used Available Use% Mounted on
none                 tmpfs         400.0M    397.4M      2.6M  99% /

If you see something like above (only 2.6 MB free space on Qts system), you can conclude that certain services can't work because lack of space. So try to remove some unnecessary files from your Qts system, like:

rm -rf /home/httpd/cgi-bin/apps/mediaViewer

and maybe more unnecessary files and folders:

/usr/share/qnas_console_install/res/font_ttf/arial.ttf

/lib/firmware/iwlwifi-cc-a0-48.ucode  (if you don't use wifi on your Qnap)

/home/httpd/apps/Samples 

/var/log/*  (but first browse the files and make sure, that there are not important to you)

10 MB of free space should be enough to host necessary Qnap services. In addition to the step, you can also restart web services as above.

Third method can be used either when above 2 methods don't work or just to quick resolve this case. Just restart the Qnap completely using ssh command 'reboot' or use Power button or just unplug power cord from QNap and then connect it again. In my case it helped. Please remember when Qnap has too low memory (1-3 MB), you shouldn't be able to reboot the Nas. There will be message on the screen 'Rebooting system' that will last for ages. In case you have the Qnap in remote datacenter, a personal visit in the datacenter may be necessary.