La lengua de estos forum es inglese. Non se español bastante bueno por ecrir un repuesta en español.
(The language of this forum is English. My Spanish is not good enough for replying in Spanish.)
You should look for a different way to import these files. If you google around, you will find no end of people having problem with the ACE provider. It it is intended for interactive use, and not for being called from a service. I guess what happens is that Excel remains open after the seventh file.
There is the import/export wizard in SSMS for the simple stuff, and you can use SSIS when you need more automation. Other options include writing a program that reads the Excel file and inserts the data. Doing it from SQL Server is difficult. It works sometimes - but when it doesn't your kind of hosed, because it is difficult to troubleshoot.