[imp] Getting Errors while Composing

[Ted Brown]

Hello

I have recently installed IMP, I can logon to my mail server and check my
email.
Everything is working except when I try to compose an email and then I try
to send it, it would give me this error message "There was an error sending
your message: unable to set sender to [user at xxx.com]"
I have checked my logs and this is what is shown,

Jun 26 05:42:49 HORDE [warning] [imp] unable to set sender to [user at xxx.com]
[on line 931 of "C:\web\html\horde\imp\compose.php"]
Jun 26 05:43:53 HORDE [warning] [imp] unable to set sender to [user at xxx.com]
[on line 931 of "C:\web\html\horde\imp\compose.php"]
Jun 26 05:43:56 HORDE [warning] [imp] unable to set sender to [user at xxx.com]
[on line 931 of "C:\web\html\horde\imp\compose.php"]

I have tried other web clients (they worked fine with my mail server) but
IMP seems to offer the most but it is also the most problematic to install.
:-) I am at a lost on what to do, I am not much of a php programmer, any
help will be appreciated. Thanks in advance.

Apache 2.0.49
PHP 4.3.7
Mysql 4.0.2a
Horde 2.2.5
IMP 3.2.4
Win2k