No problem downloading files with these accented characters in here so I suppose the problem is related to Unicode file names.
Some changes have been introduced to handle Unicode file names, and these accented chars will produce that error if using an early, before changes, database index.
If you are using a database index done with a previous PDFE version, try with a new index. Open the database editor (Database>Edit), select the tree root entry and click Delete, confirm operation.
Now reindex all your PDF's again, using the usual DiskTree scan mode, and try again with the web interface.
Let me know if the problem persist.