First of all, be aware that resizing your hard drive partitions usually destroys all the data on them. Be sure you have a backup and restore procedure worked out before you proceed.
In order to resize a hard drive partition non-destructively, all the data must be contiguous on the drive. The best way to achieve this is with a disk optimizer, such as Norton Speed Disk. Optimize your drive, and try again.
Also, the FileSaver extension of Norton Utilities can prevent you from re-sizing a partition when one of its (invisible) files is open on the hard drive. Be sure that FileSaver is turned off, restart, and try again.