Too many received headers

This is the mail system at host mailhub20.cotas.com.bo.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
                   The mail system
<xxxx@cotas.com.bo>: host mail.cotas.com.bo[192.168.2.158] said: 554
    Too many received headers - possible loop (in reply to end of DATA command)
Final-Recipient: rfc822; xxx@cotas.com.bo
Original-Recipient: rfc822;xxx@cotas.com.bo
Action: failed
Status: 5.0.0
Remote-MTA: dns; mail.cotas.com.bo
Diagnostic-Code: smtp; 554 Too many received headers - possible loop
==============
SMTP_Server_Error_and_Status_Codes.pdf
http://www.pcreview.co.uk/forums/messages-bouncing-back-t3221669.html
The 554 error code means the transaction failed between the sending and receiving mail hosts. That occurs during the mail session between those hosts which means the message was never delivered to the recipient's mailbox. Either you (via Outlook, add-ons, or e-mail interrogative software) have mangled the headers or your sending mail host did the mangling. Or the receiving mail host is sending back a poorly worded comment to the 554 error code and something else really happened during the mail session between the mail hosts. One cause is the receiving mail host causes the message to loop back to the sender and gets stuck in a routing loop (adding more headers on each loop) which means the sender's routing tables are screwed up for the recipient's domain. The recieving mail host probably pukes after the header size exceeds something like 32KB and rejects the mail session.
You can't fix that problem. Tell your e-mail provider about the problem. It is possible that the problem is caused by your anti-spam program. I've seen them pad tabs to the end of headers which eventually make too long the length for a header. If it is to just one domain and its mail host then it is probably a problem with your e-mail provider and they'll have to fix it.
------
http://support.microsoft.com/kb/284204/en-us
UnderstandingEmailErrors/ 
Abajo sigue el texto que mando y 
tan sólo NO reciben los usuarios de la central de correos @cotas.com.bo:
Oferta de Servicios Informáticos BRB

Estimado Sr. | Estimada Sra.,
ofrecemos

   - reparación y configuración adecuada de sus PC,
   - configuración de redes funcionales,
   - venta de *equipos para uso empresarial* y
   - otras soluciones especiales (Pseudo-servidores reales***, Política de
   Seguridad de Datos, etc.)
   - Mac-compatibles con RAID
   - NAS con 8-16 TB -guardar y compartir archivos 100% seguro (MS Windows,
   Mac OSX, GNU/Linux, Unix, BSD)
   - Plataformas empresariales (GNU/Linux o Windows)
   - Soluciones bajo una Política de Seguridad de Datos

Siga el siguiente vínculo:
Oferta para Empresarios
 
 Y si quiere leer en un contexto más detallado:
Información general

Estamos seguros de ofrecerle un servicio a la altura de sus expectativas
Si requiere considerar algún caso especial de Seguridad Informática o una
solución adecuada a su empresa, no tenemos ningún inconveniente de visitar
sus oficinas para tratar el tema personalmente con la persona indicada.
Atte.
Carlos E. Bähren
77644057 3281202
cebaehren@gmail.com