I'm playing 0.30.1G and it was an initial install. During my early fights with the rats, I was able to use mana and health potions without error. Just when I reached about level 3 or 4, it suddenly started happening and without any errors being displayed or a request to 'ignore'.
So to understand the fix...
(1) from the appdata folder, I'm to delete just the persistant data file
(2) from the main game's folder, I'm to delete the contents of the save folder (what about the sync folder within the save folder?)
As an interesting note... during battles, I can use the 'cure poison' and the 'increase health and mana' (the green and pink vials). Just can't use the red or blue vials that increase health or mana respectively.
Thank you for the prompt reply and sorry for my delay in responding.