Error Resizing Partition

[klear6]

Trying to partition my external hard drive for use by two people. I need to split it basically in half. It is a 2.72 TB NTFS (actual space not advertised space) external Western Digital "My Book." I have used 1 TB (almost exactly, I just noticed) leaving 1.72 TB free. I am trying to use EaseUS Partition Master 10.8 on a Windows 7 PC. Every single time I try, I get a message saying that there was "some error" resizing the partition and it reverts right back to the way it was before. I need separate partitions because I would like to avoid harming or in any way touching the part of the disk that is used by the other person as much as possible (and vice versa). So far the only data stored on the disk is my own. What's the deal here? I would give more information on the error but it actually just says it encountered "some error." So, if you need more info, please ask and I will tell you all that I can! Also, the other person using the drive has a Mac and I need to know the best file system to use for them, if it is not NTFS.

 

[Ironsounds]

Hello... the Partition is currently active in the Windows7 OS... and security levels/settings/permisions can interfere.
1) try marking the partition "not active" first.
2) Doing "Disk Tool" operations are best done at a basic DOS level... Outside a Windows OS.

 

[klear6]

K awesome, thanks. I don't remember the commands but my husband does. I will try that later - I'll pick your solution as soon as I get it to work, till then I will leave it open in case someone else has input =) Unless you want to to tell me the commands.
Mark as not active
Resize the one with data on it to (half of 2.7ish)
Create the new one
(I think that's all I need to tell it to do right?