Rendering and Save error

at rendering time I get an announcement saying that an error has occurred “Could not open file: C: / Users /(…)/ Documents / toon boom harmony premium library / (my document) / frames / preview - (. …) to write”, see the attached image, the same goes for the save where it says an error occurred with the" frames "

PS: my file is called “callese”, not to be confused

Please help me, this is confusing me