can´t attack a file to this message!Can you help me?

[Foratog]

Hi,when i write this message to you help me to solve a problem in my computer,i wanted to attach the file "hijackthis.log" to this message to you see what´s my problem.But it not leave me to attached it!Well,i change the name of the file to "hijackthis.txt"...it not leaves me to attached it!Why?And how can i solve my problem without hijack´s log?Many times I tried to attach it to this message in attach management.Thank you.