Hi,
The Messages app is one of the ones that is Sandboxed.
This tends to mean the app is set up in a way that a crash will not bring down other apps.
This is reality means that the app has a Read and Write path (~/Library/Containers/com.apple.iChat/Data/Library/Messages And then an Alias for a folder called Attachments), And a place where it actually stores the files that your are sent (~/Library/Messages/Attachments)
If, for some reason you have lost Read and Write permissions to any of the containing Folders then you will not be able to store the item being sent to you.
Use the Finder window.
Use the Go Menu whilst holding down the ALT key.
Select the Library that appears in the List.
Select CoverFlow view if you are not already.
From the Finder > View Menu > Show Path Bar (this shows icons of the folder across the bottom of the window).
From the View Menu > Show View Option choose the Modified column option.
Navigate to Messages/Attachments.
In the Path Bar right click the icon for the Messages folder and select Get Info.
Scroll to the bottom of the info panel.
Your Short name should appear.
Select this and Unlock the Padlock
Now use the little Cogwheel icon.
This should show that you Own the file by being greyed Out.
If required make it that you do Own it and also apply this to the Contents.
Repeat for all the folders in the other path involving the Contains folder.
It is long winded and time consuming but it is a less of a sledge hammer approach.
10:16 p.m. Wednesday; August 12, 2015
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad