Can't read the files used for encryption between site and paypal

I have a strange behaviour. But I am not sure if it is a bug or if I made something wrong. Let me describe the behaviour:

1. Under the path 'root/production' of my hoster I developed my productive site which works 100%. If I go to the CB Subs productive Gateway in the backend all the necessary files needed for encryption can be read...and also the payment by credit Cards (via PayPal) works excellent....see below the screenshot (remark: the productive site is built with CB Subs: 3.0.0)



2. In order to upgrade the productive joomla site, I copied the whole productive instance to the path 'root/pre_production' ....here I also upgraded the CB Subs component to 4.1.0....the problem is: When I go to the CB Subs productive gateway (in the backend) it seems that the necessary files neede for encryption can not be read (remark: in both cases I reference to the exactly identical file folder...so it cannot be an Access right Problem (see below) .....Even if I copy the whole instance from 'root/pre_production' back to 'root/production' the files are not readable...see below

That sounds entirely like a server permission problem. Ensure the folders and files have the same permissions when you copied them over as the originals and be absolutely sure the paths are correct.

I have absolutely no idea where the problem is..my setup is as follows:

folder: /joomla/prod_paypal_certificate

....in this folder I have the 3 files: idp-pubcert.pem / idp-prvkey.pem / paypal_cert_pem.txt

Env 1: folder: /joomla/production

...in this folder I run the productive website....and the cb subs gateway refers to the files in: /joomla/prod_paypal_certificate
..and all 3 path are checked with green colour

Env 2: folder: /joomla/pre_production

...in this folder I run the test website....and the cb subs gateway refers to the identical files in: /joomla/prod_paypal_certificate
... but here all 3 path are checked with red colour

...so with both installations I refer the same folder (/joomla/prod_paypal_certificate) and I used in both cases exactly the same path string ....the only difference is that /joomla/production runs with CBSubs 3.x and /joomla/pre_production with CBSubs 4.x ....???!!!???

Try copying the certificate files to the following.

/joomla/pre_production/prod_paypal_certificate

Then using that path.

I believe it is a server ownership/permissions issue:Also check the file owners in addition of permissions.

Usually copying files on a server keeps ownership

ls -la

to see ownership corresponding to website.

...I tried to do so and copied all 3 files from:

joomla/prod_paypal_certificate

to...

/joomla/pre_production/prod_paypal_certificate

...but it didn't help, so I made the following test:

I copied the whole joomla instance under:

..../joomla/production ....... /* which is running correct and has CB Subs 3.x installed */

to a totally new location under

.../joomla/testenv ............../* I deleted all the files in testenv, and created a new db - the backup image was made with Akeeba backup tool */

So the result was, that the /joomla/testenv installation was also working 100% (correctly refering to the same files under joomla/prod_paypal_certificate) ........so from my point of view this is the proof that it is not a path or a server access right problem.....the only difference is that my instance under /joomla/pre_production is built up with other component versions (e.g CB Subs 4.x / etc) ...for some reasons this instance seems to be corrupt, but I do not know why ??? there is no warning if I enter the backend in joomla/pre_production