If the subreport is in the Page Header, move the subreport to another section of the report.

If the subreport is in a Group Header and the group has the "repeat group header on each page" option marked, un-mark this option.
  1. Right-click on the Group Header and select Change Group
  2. On the Options tab, un-mark the "repeat group header on each page" checkbox
  3. Click OK