vCenter Error: Another task is already in progress

I got this error message ‘Another task is already in progress’ when I tried to take a snapshot of a Linux virtual machine. To troubleshoot it,  I checked the tasks and events tab of this virtual machine and found someone was trying to upgrade the VMware Tools at earlier time Today but failed. I guess this could be the issue. To confirm it, I right click the VM and choose Guest. It shows ‘End Install/Upgrade VMware tools’. Ah, now it makes sense – as the installing/upgrading VMware tools is hanging there, which of course leads to the failure of taking snapshot. To solve it, just simply end the install/upgrade process, then take snapshot again. As this is a Linux server, I guess that guy probably does not know how to install the VMware tools in it properly. The right process is to choose install/upgrade VMware tools first, then login into the Linux box to mount the /dev/cdrom and copy the installation package somewhere. Then run the Vmware tools installation script.

I did some further research on this error, it may occur as well when the vCenter operation times out.  (See more)