I just drag'n'dropped from a stack, and back to a stack. no problem.
killall Dock
Is it working? If not, put the dock plist back. If it is, there is a corrupt entry. Rebuild your dock from scratch.
If that doesn't work, report back.
Also, is the stack built from a folder or is it one of the "Recents" stacks? If the latter, you cannot drag and drop from those stacks.
This has been the case since the SL install as far as I can remember (this was a few weeks ago) so have tried the steps above but even a dock with a fresh plist still refuses to drag and drop. All stacks are folders (Downloads, Apps, Documents, some I dropped in the dock myself,...) and all display the same behaviour (or refusal to behave).
What exactly do you mean by rebuilding the dock from scratch?
Also, I'm using a custom dock background, but this shouldn't affect the functionality?
I guess what i mean is i'm using SL 10.6.3 and it works fine.
https://forums.macrumors.com/threads/89736/
And try OnyX
I take it you upgraded over the old OSX, not a clean install? And have you completed any updates.
What I meant is that if removing the dock plist works, you would just have to rebuild your dock to your liking.
I would consider the custom dock background as a potential problem. Restore to all default settings. If that doesn't work, create another user and try it there.
Do you have any 3rd party add-ons that alter or add to the Dock's functionality?
-> Additional info: 2Ghz 2Gb mini running 10.6.3. (clean install)
Have used Onyx since the install to check disk. Could run it again and see if it fixes anything. Thanks!
No other add-ons that affect the Dock. And the customised is literally just that, a different background. I'll try a different user account, also run Onyx and then report back. Thanks for the quick responses so far!
I understand that it is simply a different background, however, since your dock is modified I would look to restore the dock to stock to rule that out.