For a long time now, everytime I move a message from my inbox to another folder, I get this error. Closing eMClient and starting again will sync and correct the problem. I cannot figure out what is happening. I use hMailserver as backend.
Can live with it, but seeing this fixed somewhere in time would be great 
Problem solved, just recieved an update and changed some settings connecting to the server 
Hi Erik,
I’m glad the update fixed the issue for you, thank you for letting us know.
regards,
Olivia
Hi, I am having the same problem as Erik and am using em client ver 6.0.26162.0. How did you fix this? Thank you!
Is that a recent version? I’m on 7 right now. Do you host your own server? That was part of my issue as well…
My email server is Google Apps gmail on IMAP. I upgraded to the most recent of the revision 6 series em client. Customer support did a remote session with me and confirmed my settings and version are correct.
Welcome to the world of IMAP… I would suggest a downgrade to a previous version in order to figure out that it is EmClient or upgrade to 7. Which has a free edition as well as 6. I forgot what 6 looks like, I was used to 7 in like one minute?