RMAN-06172: no AUTOBACKUP found or specified handle is not a valid copy or piece

You might see this error when  you lost your SPFILE and try to restore it from autobackup.

Solution.

RMAN> restore spfile from autobackup recovery area='+RECOV' db_name=ora11g;

+RECOV is my flash recovery area resides on ASM. If you haven't configured ASM, you should use absolute path of FRA.

If you are sure that there is an autobackup, Find it's path.
If you have configured ASM, This would usually be at +RECOV/ora11g/autobackup/<latest_date>

For Ex:  +RECOV/ora11g/autobackup/2012_01_07/s_771966441.386.771966443

Then you can restore your SPFILE using

RMAN> restore spfile from '+RECOV/ora11g/autobackup/2012_01_07/s_771966441.386.771966443';