Sporadic delivery of reports

Hi,

Have set up two very simple custom reports to be emailed in an html format to two addresses (comma in the middle). Can not understand why delivery works for awhile then stops. I log back in,  "Send a Test Mail," and "Run Now". All which works great. Then i will receive for a week or two, and then it stops. Have repeated this for months now, since i bought the software.

Any assistance would be appreciated—Jeff.