I deleted unnecessary diff files then 'Specify location of the volume' appeared

-- 3rd --
I could delete a differential backup No.5 from True Image User Interface.
Then I double-cliced No.8 in Windows explorer, but 'specify location of the volume 5' window still appeared.
I think there aren't any difference between deleting from TrueImage and from Windows explorer for this point.
So I'm thinking delete differential files from Windows explorer which I cannot delete from True Image User Interface.
When I deleted some the younger number differential files (No.5) then I double-clicked the older differential file(No.8), 'specify location of the volume' window appears.
I couldn't avoid this problem, so far.
In this situation, if I deleted many differential files I don't need, are there any problem?

Thank you in advance,
Ken (Japan)

Version : Acronis True Image Home 2010

-- 2nd --
I found a solution in the help file.
It said that you should use True Image to delete differential files, because tib file has metadata database.

So, I tried to delete a differential file (No.3), but it didn't work.
Window for deleting didn't appear.

But if I selected No.8, a window appeared.

It seems that there are some backups which I cannot delete from True Image.

Could you tell me how I can delete those files?

--- 1st --

From now, I want to delete unnecessary differential files.
For example, I have created one full backup (No.1) and eight differential backups(No.2 to No.8).

Phenomenon-1:
As a test, I deleted No.3 then I doublecliced No.8 diff file.
A window appeared with the warning message like 'specify location of the volume 3'.
I clicked 'cancel' twice then 'backup explorer' appeared.

I think when I recover partitions from differential backup, what I need is one full backup file and only one differential file.

I'm going to many unnecessary differential files, so I would like to make sure the meaning of Phenomenon-1 before deleting the files.

Can I recover the partition images from No.1 and No.8 properly with all the others deleted by DVD booting, even if the warning message appears like Phenomenon-1?
(I guess this warning will appear 12 times if I deleted No.2 to No.7.)

Is the Phenomenon-1 abnormal one to avoid?
Are there any ways to avoid the problem?

Thank you in advance,
Ken (Japan)

Version : Acronis True Image Home 2010