Any layer in a group layer that has a hyperlink field set is not being honored by ArcReader at versions 8.2 and 8.3.
The hyperlink tool does not work correctly with group layers at ArcReader 8.x.
This problem has be fixed with the release of ArcReader 9.0. Hyperlinks are now supported in group layers.
An alternative for 8.3 users would be to move the hyperlink layer out of the group layer prior to publishing the published map file.