In all versions prior to 3.0333.4 the file paths for Icons shown in the Recently Viewed List and in the Favourites List are encoded for security purposes, which can make their length greater than 255 characters, which was the database column length to store the path from the Asset Types Form and in other places, where the path does not have to be retained on the client side. This means that, if you do have long paths to Icons for Asset Types and other Standard Objects, you could experience an overflow error.
The problem is fixed in version 3.0333.4 and requires the database to be upgraded to version 3.3. The upgrade is optional and only necessary, if you have the overflow error.