Could you please check if there is any grammatical errors in this sentence?

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I hereby inform you that while waiting for confirmation from the Hotel A about the possibility of 6 days reservation for His Excellency, in order to attend the SAT Conference in November 8th to 14th, 2007, in a backup, we have also reserved hotel accomodation during those period for His Excellency with the Hotel B, of which the room types and rates are attached.

It should be "six days' reservation" (one does not use the numeral in formal correspondence). The other problems that I see is that it should say "as an alternative plan," and "we have also reserved hotel accommodations during that period..." and "for which the room types and rates are attached."

Could you please check (to see) if there (are) any grammatical errors in this sentance.

Two...

nope

It's a run on sentence, and too complex. Try this re-write on for size.
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We are awaiting confirmation from Hotel A for a 6 day reservation for His Excellency to attend the SAT Conference November 8th to 14th, 2007. As a backup, we have also reserved hotel accommodation for His Excellency for the same time period with the Hotel B, for which the room types and rates are attached.

I hereby inform you that while waiting for confirmation from the Hotel A about the possibility of 6 days reservation for His Excellency in order to attend the SAT Conference in November 8th to 14th, 2007, as a back up, we have also reserved hotel accomodation during this period for His Excellency with the Hotel B, of which the room types and rates are attached.

Changes = took the , out after Excellency. Changed 'those' to 'this' and it should flow so you could read two parts like this

"I hereby inform you that while waiting for confirmation from the Hotel A about the possibility of 6 days reservation" ... "as a backup, we have also reserved" (etc.)

If you can make it shorter by possibly moving the "in order to attend the SAT Conference in November 8th to 14th, 2007" to the end of the statement it would make it easier to read, so say you could write out the second hotel reservations then, "regarding the matter of the SAT Conference in November 8th to 14th, 2007".

There are a few mistakes. A better way:
I hereby inform you that, while waiting for confirmation of the 6 days reservation for His Excellency from Hotel A, we have also made reservations at Hotel B as a backup in order to ensure accommodations during His Excellency's attendance at the SAT Conference being held November 8-14, 2007. Attached are the room types and rates.

Please be advised. With regard to His Excellency attending the SAT Conference commencing November 8, 2007 confirmation is being sought by Hotel A and Hotel B.

Please find attached rates and accommodation information for each Hotel for the period 08/11/07 - 14/11/07.

... are you asking them to choose? or are you covering your options? ... just wondering ?