C# - Error Creating A User With More Than 20 Chars In SAMAccountName Using .NET?

I'm trying to programatically create a new Active Directory user setting the sAMAccountName attribute with a value larger than 20 chars.

When I call the DirectoryEntry.CommitChanges(), I get the error:

00000523: SysErr: DSID-031A0FB6, problem 22 (Invalid argument), data 0

If I try to create a new user setting the sAMAccountName smaller than 20 chars everything work.Before someone says the the limit of the sAMAccountName is 20 chars, I want to point out that if I try to create the same user having the sAMAccountName more than 20 chars using the Windows tool "Active Directory Users and Computers" everything works. I can see the new entry in AD using the LDP tool and the entry has the sAMAccountName with more than 20 chars.Why can't I create the user programatically using .NET?

Below is the code I'm using:

Using objDirEnt As DirectoryEntry = New DirectoryEntry("LDAP://my.domain.com/cn=Users,dc=my,dc=domain,dc=com", "username", "Password", AuthenticationTypes.Secure Or AuthenticationTypes.Sealing)
Using usuario As DirectoryEntry = objDirEnt.Children.Add("CN=aaaaaa bbbbbbbbbb ccccccccc (aaaaaa.bbbbbb.ccccccccc)", "user")
usuario.Properties("sAMAccountName").Value = "aaaaaa.bbbbbb.ccccccccc"

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