Hi,
[quote]Could those gaps be the origin of my error messages? Where do those gaps come from? Is there a way to fix them?[/quote]No they are normal occurence and should result in nothing more than a little bit of wasted space on disk. The only way to get rid of them is to rewrite the file making absolutely sure that no key is ever deleted (i.e. you need to disable the TTree Autosave mechanism).
[quote] I tried to exchange the files with error messages but the error still remains.[/quote]What do you mean by exchange?
I noted that in your example the same exact error is repeated twice. Is there error in other files and/or in other places in the file?
Philippe.