I have this issue sometimes when taking snapshots, when I try to upload it to my hard drive the upload will fail, or simply get stuck on the open save window not finding the proper folder to save itself to.
Which can be a pain, it usually is solved by a relog, but I have spent half an hour setting up a pose, messing with windlight, getting the shadows just perfect and when i´m about to snap it fails on me, a relog would involve seting everything up again and trying to catch that perfect angle.
But there is a workaround I sometimes use when this issue happens, instead of saving to my hard drive I post the picture on my wall, also available from the snapshot menu, and later download the picture from my wall to my hard drive. It´s simple and works perfectly, saving the picture in it´s original size, this simple tutorial shows how to later after all pictures are taken, recover them from your wall. You can either access you wall by clicking the links that will show on your notices saying the picture is available, or by your SL Dashboard, note this will not work if you try and do it from your profile inworld.
1- Log in to the second life website, or click the inworld link that will appear as a notice saying the snapshot is available.
2. Click on My Second Life highlighted in red on the picture above. This will take you to your profile wall.
3.You can then see all the snapshots you uploaded on your wall, as you see snapshot is highlighted (marked in red) and you can click it.
4. This will show your picture slightly bigger, by moving your mouse over the picture the option to see it full size will show up at the bottom as highlighted in red on the Picture above, by clicking it a new window or tab will be open in your browser, showing your picture in it´s original size.
You can just later delete the picture from your wall if you wish so or leave it there to share with your friends.
I hope this was helpful.