While migrating from D6 to D7, the function simplenews_update_7000() threw an error because I was trying to insert a string with 71 characters into a field which only allowed 64 characters. I personally feel that 64 is too short a limit, especially in languages which are more verbose than English (in my use case, French). Further, this will break the upgrade path for anyone with a longer from_name in D6. So, I propose reverting, changing the schema of the table simplenews_category, and changing simplenews_update_7000() accordingly.
If you really believe that this field should be limited to 64 characters, simplenews_update_7000() should truncate this field and print a warning instead of throwing an error.