Unable to backup after recovery model change
In SQL Server you have 3 forms of backup: Full, Differential and Log:


The Full backup is the most important because it has all the information of the database.
The differential is the diference of the last full backup until now.
The Log is the diference of the last full or differential backup until now.


So you can have just the Full Backup or Full and Diferrential or Full and Log or Full, Differential and Log backups. You choose the best combination for your need.

Also look for the recovery/nonrecovery option in the restore clause