>This is related to the Task.Log field. When this field is included in the SQL command, it is slow. This field is a Varchar(MAX). For 43 records, it contains the log of the last process of each task and that can be somewhat be considerable like a few K for each. I still do not understand however how this can be a factor. I have the same on other tables and this does not affect. I believe this might be related to data corruption or else. This Task.Log field is updated every minute. So, basically, it replaces the old value with a new one. Can this really be a problem?

Check this new article http://social.technet.microsoft.com/wiki/contents/articles/19670.t-sql-useful-links.aspx#SQL_Server_Internals

Go to the 3rd article in SQL Server Internals section - to the article by Paul White. It may help you.