How to use Archmage's SLA?

[william_iii]

Gain a level of Archmage, choose SLA feat, and a new icon appears in the radial menu. When clicking the SLA icon, I'm told that this SLA hasn't been stored, & the next spell cast will be stored. Then I cast a spell but nothing happens. The number on the SLA icon just turns from 1 to 0, and after a rest it returns to 1. None spell-like abilities seems to be gained.

So what is happening 

[xwarren]

Which spell did you tired to assign as SLA? Which class?

I just checked it with my beguiler character and shadow shield spell - seems to be working fine (you just need to cast the spell within 18 seconds after you use the feat).

[william_iii]

Which spell did you tired to assign as SLA? Which class?

I just checked it with my beguiler character and shadow shield spell - seems to be working fine (you just need to cast the spell within 18 seconds after you use the feat).

18 seconds... that's the point...

Thank you once again, xwarren!