Do you remember if you ever created an empty spell scroll ?
It is possible to destroy important quest scrolls this way, because for the crafting system, they are just a normal piece of paper.
I'am playing mage and i created some scrolls.... Is there a way to solve this problem?
Not really, the only thing you can do is to be careful and craft empty scrolls only from the experiment page of the crafting window where you have complete control over the ingredient input. Crafting from the recipes page is dangerous in this case because the crafting engine cannot distinguish between a normal sheet of paper and a quest relevant sheet of paper. For the crafting engine, both are the same.
Unfortunately, there is no way to get the letter back if it was destroyed this way. Loading a save before that point would help of course but if it was really destroyed through crafting, one cannot expect you to remember when the scroll was crafted.
I'm not sure how big of a problem this is considered at Larian and I have some doubts that there will ever be another patch which could fix this. (Currently they are way too busy with D:OS2 and there have been rumors a long time ago about yet another secret project. There seem to be enough changes in D:OS2 that they might even get problems understanding their own game at some point because they are not used to the 'old way of doing things' anymore, but we'll see ;-)
I hope to get a mod out soon where I have changed this - among other things. But that does not help you in an already running game of course.