Computer:  servername
Source:       VolSnap
Category:  None
Type:         Error
Event ID:  25
Description: . 
Consider reducing the IO load on the system or choose a shadow copy storage volume that is not being shadow copied.

Resolution:

Note: Always take a backup before making any changes.

Check where the Shadow Copies are located and the current size of the shadow copy cache. To do this, logon to the server which is reporting the error.
Click start, click run and type vssadmin resize shadowstorage, press enter. Check that you have enough disk space.

Next, increase the size by amending the registry as follows:

1.     Click Start, click Run, type regedit, and then click OK.
2.     Locate and then click the following key in the registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VolSnap
3.     On the Edit menu, point to New, and then click DWORD value.
4.     Type MinDiffAreaFileSize, and then press ENTER.
5.     On the Edit menu, click Modify.
6.     Type the size that you want for the shadow copy storage area, and then click OK