PBIRS (march 2018) is having trouble handling certain (all?) non-standard ASCII-characters in folder names. When a folder contains non-standard ASCII a new report gets the name converted to all lower case. If the name of the report is corrected then the report cannot be updated/overwritten from PBI Desktop RS without getting the error "Sorry, you don't have the permission to save in this folder".
How to replicate:
You will also run into the similar problems if the report's name contins these characters.
This makes it quite annoying to update reports that are saved in PBIRS. The workaround is to
The collation of the report database (PBIReportServer) is Latin1_General_100_CI_AS_KS_WS
Hope this can be fixed!
I actually found a bit easier workaround that doesn't include delting the report from PBIRS. Instead, choose Manage report and change the name to be only lower case letters (I'm not sure this goes for all the folders as well). After this the report can be saved and after that the report name can be changed back to whatever the name should be. This way the report is not deleted and keeps the same reportid which is useful when collecting usage statistics.
The problem still exists in January 2019 release - I opened an "idea" for bugfixing it: