I experienced the same when I tried to send SMS from Outlook with a Gateway software. The software somehow did not update which e-mail was sent and which was not. I followed all instructions again and it solved now. I dont know which config step was missing but after I reconfigured it worked well. Maybe you can get some idea from this site (I followed this)
http://www.sms-integration.com/what-...t-work-94.html
hope it helps
Anton