OpManager sent an alert with wrong information regarding disk space

OpManager sent an alert with wrong information regarding disk space

Hi,
 
OpManager sent an alert with wrong information regarding disk space. When I checked the server disk space it is still 27.7GB and OpManager sent a zero disk space alert. This happened twice on different server and need to configure again the servers on OpManager. What causing the problem? Please help.
 
 
 
 
Regards,
Joel