When you use Convert.exe to convert a file system from FAT, or FAT32, to NTFS, Windows issues:
The type of the file system is FAT\[32\].
Determining disk space required for file system conversion...
Insufficient disk space for conversion
The conversion failed.
<Drive:> was not converted to ntfs.
You know that you have enough available freespace?
If you have bad sectors at the end of the partition, this error will occur.
To determine if this is the cause, perform a chkdsk <Drive:> /f /r on the partition. If one of the lines contains nn KB in bad sectors, bad sectors is the likely cause.
To workaround this issue, backup or copy your data on this bad partition, reformat as NTFS, and restore your data.