TMC²: Cannot open File

[proma]

When I have a manialink where I can pick a file for upload and press the upload button then this error message appears. This only happens to me, my friend can use the same manialink regularly. Also when I open the file selection dialog the default folder is the topmost folder of my personal TMC data (which is intended) but most of the folders inside this one are not displayed and even worse map files (map.gbx) are also ignored. Did anyone encounter similar problems?