Well depend on what you are really doing, there is deleting and deleting,… First one is copy & paste first, in this case there is necessary to have appropriate free disk (quota) space available. By Occam’s razor this is what is wrong,…
If it is not this case than in eM Client you can set up diagnostic logging and check logs. Also you can extend logging on server side too, maybe something like I wrote here and as always go to docs,…