I made sugar cookies and iced with an outline of royal icing and filled with thinned royal icing. I have made these before ( even in the summer) and for some reason the icing is not drying. I am unable to package them or stack them at this point and they have been in the freezer and at room temp. for over 48 hours now. What was my mistake? I don't want to repeat it...there must be a trick to thinning royal icing...I used water.

Did you put the wet iced cookies in the freezer???

Sometimes high humidity will affect how long it takes for them to dry. I usually put a fan on mine to dry them and they are ready to stack after about 12 hours but no more than 24 hours.

A dehumidifier will help take moisture out of the air.
Sorry that's all I can offer. Not sure why they aren't dry after 48 hours. Using more water shouldn't affect them that much.

I am no expert, but here are some things that I do. First, I use Antonia74's RI recipe and as recommended, use water to thin the icing, but only enough to get it to do what I need as adding water will increase your drying time. If it is humid, I make sure the a.c. is on and once the cookies are done, I put them under a light if I am in a rush to dry them. I use a high powered work light we have for remodeling and it really does the trick, but you need to give it enough time. Once, out of desperation, I turned the hair dryer on them as well, which I have now seen on CC that others have tried. I have heard of others putting them in the oven on a very low heat, but the time I tried that, the icing got a bit speckly, but that was prior to using Antonia74's recipe and it seems to have worked for others here on CC. I am sure you will get more/better ideas from your posting, but that is what I have. Hope it helps and sorry you had this happen!

Oops! Looks like I am wrong about more water adding to the drying time! The dehumidifier is a great idea! I forgot about that. My dad recommended that one time, saying that I should buy one and set it up in a room that I could close off with the cookies.