Thank you for you answer. Unfortunaltely I still cannot access the folder. I also checked the server log and could not find anything. Strangely, I have a .dsp which invokes some services within the folder I cannot access and I can use the dsp without any issues. The IS version is 8.2.
Do you have any idea where can I find the ACLs configured for the services withing the folder I cannot access?
I tried to compare the settings on the server where I encounter this issue (dev server) with the ones configured on the prod servers and could not find anyting different.
UPDATE: you can close this topic as I made a huge mistake. Before the restart there was another ACL created by a colleague alongside the one I was using which was very similar as name. I deleted the one created by my colleague but needless to say that I set up the ACL created by my colleague for the folder. I edited the acl files in the config folder and restarted the server. Thank you again for your support!