My machine only has Ubuntu installed (13.04) but one data drive is NTFS (because I didn't realize that the disk was NTFS formatted when I started using it). I now used Gparted to reduce the partition and make room for a new data partition in ext4 format so that I can move the data there instead, then delete the NTFS partition and resize the ext4 partition to use the entire disk.
After reducing the NTFS partition and creating the ext4 partition, Gparted now Gparted has an exclamation mark (top) and tells me this (bottom).
I'm asked to run Windows Checkdisk twice, but I don't have Windows installed and it's very tedious to pull the drive out of the computer and hunt down a Windows pc with SATA connectors. Is there any way for me to fix this, besides using Windows?
The NTFS data partition is not available until I've fixed it, so I can't read its data and copy it to the new ext4 partition. If I could just reliably read it, this problem might be irrelevant.
Final update and solution:
I can't accept either answer because the Linux tools could not resolve the problem. In the end, I booted my machine with a Windows 7 installation disk and started the repair/recovery function. In there, I could open a command prompt and run the chkdsk /f
which solved the problem :-)