Looks like from the steps in your action that the green channel is the only channel visible.

You probably need to put a step in your action to select rgb channels  to be able to add an adjustment layer in action.

If we knew what you wanted the action to do, we could perhaps offer more helpful advice.

Make Adjustment Layer need to have a layer targeted in Photoshop.  When you select the green channel you target only the green channel as photoshop's current target some adjustments, filters and tools can be used on channels however a channel is not a layer you can not add an adjustment layer over a channel thus the error message make not currentle avalible.  Targeting the RGB is actually targeting all three channels so the current layer becomes the photoshop target when select RGB channel is used.

When you do it manually by any chance do you click on the layers pallet tab so you can see the color image not the grayscale channel you been working on? If so clicking on that tab is like clicking on select RGB channel.  No I see your right you can do it without selecting the RGB of Layer palette perhaps Photoshop should record a select RGB because it does do the you the color layer after adding the adjustment layer.  I would say it is a Photoshop bug and has been foe many releases. I just tried the test in CS2 the oldest version I still have installed it has not ploclen addint the adjustment layer without selecting the layers palette or RGB channel.

I don't think that is a bug.

Although it is interesting that versions of photoshop before photoshop 6 do record and play the the action as expected, but versions after photoshop 5.5 produce that error, so it

does make one wonder about the change.

Not true.  Actions should pay just like they were recorded when played on a similar document.  Let make it easy open a new default document. You know a single white background layer.  Record the action on this document. Then close the document no save.  Open a new default document play the action is should work like it was recorded without error like when recorded.

The sequence of steps to produce the error is quit simple you only need to do three things while recording the action.

select green channel

gaussian blur radius 1.2 px

add adjustment layer a default curve for example.

During the recording of this action Photoshop does four things but only records three. Before adding the Adjustment layer Photoshop switches from viewing the green channel to the layer the RGB channel  (which should recode select RGB Channel) and then add the Adjustment Layer, for your viewing the color image after the adjustment layer is added and the active channel in the channels palette is the Adjustment layer's layer mask. Lets say I'm wrong it did not switch to the RGB channel then you will also see that menu layer>New Adjustment Layer>Curves... is valid for it is not grayed out and it works while recording the action. The adjustment layer is added and recorded as make adjustment layer.

The action recorder does not not record a switch with Select RGB Channel and when the action player tries to play the third step Make adjustment Layer fails with the error message make not currently  available. Why??  And why if you inserts a select RGB channel before the make adjustment layer then the action works.  Actions should play like they are recorded. When recording an action if Photoshop switches from a single channel to the RGB channel that should record select RGB channel or because menu layer>new adjustment layer>curves... is not grayed out when the green channel is the selected target and works manually so its available. Why then does Photoshop pop-up the message Make currently not available when the action step tries to execute.

This is not a new bug it in all versions of Photoshop I still have installed. CS2, CS3, CS5 and CS6....

The action recorder job is to record everything that you do that is recordable.  If adding a adjustment layer is recordable when a channel is the current target like it is recorded.  Why is it not available when an identical document is in the same state with the green channel target why is it not possible to do. Its because something is rotten in the code.  If I stop the action I can add the adjustment layer but I can not play add adjustment layer. Why is it available to me but not available to the action player. I have told Photoshop to make adjustment layer and it does. The Action player with the same document in the same state tells Photoshop Make Adjustment layer and Photoshop pop-up not available.  I;ve reduced the action to two steps. Select Green Channel ans Make Adjustment layer.  Possible to do is Photoshop not possible in a Photoshop Action. Rotten simply rotten...