Error Message when trying to start Drastic on my Android

[DasEnormeLineal]

Hey guys,
I hope someone can help me. I have a Sony Xperia Z3 with the latest Android Version on it. Last time i used Drastic it worked totally fine. Today I opened it and the following error Message occured:
Drastic couldnt write on the following path $path$. Please Check the free intern storage and make sure you got write permission for the path. Also try to restart the Phone.

Do you have any idea what to Do?
My Phone isnt rooted. There is over 2GB of free storage. I payed for the app. Permission is enabled for Drastic. Already reinstalled the app. I dont know what else i can try.

I would be thankful for any help!

[Exophase]

Are you sure that the 2GB free is on the internal storage, and not on external SD card storage? It could also be that somehow write permissions were lost for the directory.

[DasEnormeLineal]

Yup there is enough free storage. The thing is that i can still install apps and they are also working normally. How could I regain the write permission? Or at least Check if it is missing?