Page Layout ⇒ Chapter in the head of the page

[localghost]

[...] But , I wonder why I should take them out of center environment.?? [...]

It simply doesn't make any sense because these commands have not effect on the local output. They just add some information to the ToC layout.


Best regards
Thorsten

[gmedina]

...But , I wonder why I should take them out of center environment.??...

In fact, it's enough to protect[1] the \addvspace command, and it's advisable to always do so. Instead of simply

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\addtocontents{toc}{\addvspace{-10pt}}
 
 
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one should always use

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\addtocontents{toc}{\protect\addvspace{-10pt}}
 
 
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[1]Here you can find some explanation about "protection" and fragile commands:

TeX Frequently Asked Questions -- question label "protect"

The \addvspace command has some particularities and subtleties, which you can find explained, for example, in the LaTeX Companion (2nd Edition).

Addendum: for clarity's sake (and to prevent possible future misunderstandings) I will edit the reply in which I suggested the use of \addvspace for the first time, to protect those commands.

[QwareeqMathematics]

Thank You