DISCLAIMER!
I’ll take no responsibility for any loss of data or any other problem caused by following this tutorial.
Reinstall DSM (eg 5.2-5644) without losing the data on Volume:
01. Enable SSH if it`s not & connect to SYNOLOGY
02. Open & edit the file \etc.defaults\VERSION
03. Exchange the data with one of previous ver.:
majorversion="5"
minorversion="2"
buildphase="0"
buildnumber="5592"
builddate="2012/12/05"
04. Save & Exit
05. Restart Synology
06. Launch Synol