There are rules when it comes to resizing and/or creating partitions.
For instance only 4 primary partitions are allowed,
you can't partition/resize a mounted drive and so on.
More information regarding what you were trying to accomplish would help.
So would some information about the errors.
Is this your first time partitioning?
Parted Magic is supposed to be easier to use than Gparted and it
also has more features.If you want give it a try.http://partedmagic.com/
Remember more details will result in more answers.
Things are more like they are now than they ever were before.
Dwight D. Eisenhower (1890 - 1969)