Hello, my problem is similar to this one. But the advice given in that topic did not help me.
I used to bitnami-redmine-3.4.6-0-linux-x64-installer, with Debian 9.5 (stretch) x86_64 (kernel: 4.9.0-7-amd64).
I'm trying to install any plugin, but this error does not allow me to do this.
What i did: I installed debian on the server, i created the user "bitnami", downloaded the bitnami-redmine-3.4.6-0 installer and installed it in /home/bitnami/. After that I deleted the default database in MySql and installed my own. The application is working, but when trying to install plugins, at the bundle install stage, this error occurs. I found a post with a similar problem, where you could solve it, i repeated the same steps, but it did not help me.
I see no point in applying the Apache log, because the error is completely identical, but if necessary, i will do it.
p.s. sorry for my english - this is not my native language ((