Archive log restore using RMAN

Hi,

I am try restoring archivelog which is already backed up in the tape, by using

logsequence, when the system also listing first backup pieces of archlog and then it says

channel t1: reading from backup piece DWHPROD_Archive_i5mqrb5i_1_1, then nothing is happening

no restore, what could be the problem ???.. pls advice and where to check

Moreover I was trying for tag (tag name which was listed in the backup log) as follows in the script

RESTORE archivelog FROM TAG 'TAG20111123T171856'; or RESTORE archivelog FROM TAG = 'TAG20111123T171856';

but the system thro's error as follows