I have DT Pro (latest) and am running OSX Lion. I tried to place a pdf file from my desktop to an inbox and have received this: “Can’t put the dropped file in user caches folder! Investigate the problem using the Finder.” No idea what this means.
Sorry, a slightly obscure error message that we should change 
The error occurs when the Sorter cannot write to its cache folder. Try the following to see if it solves the problem:
- Open DEVONthink and ensure that every document you have stored in the Sorter has been transferred to DEVONthink.
- Open DEVONthink preferences, select the Sorter tab and quit the Sorter.
- In Finder select the menu option Go->Go to Folder and type the following ~/Library/Caches and press the Go button.
- Find the folder com.devon-technologies.think-sorter and drag to the trash.
- From DEVONthink preferences, restart the Sorter
Alan
Work liked a charm! Thanks.