There are lot of open source converter are there. I suggest MRI converter instead of this.

Or you can use 3D slicer too

dcm2nii does convert from DICOM to NIFTI-1 format. It may be that you have something in your DICOM file that causes a problem. dcm2nii works with most imaging manufacturers but the DICOM format is fluid and can have lots of additions depending on the imaging modality and the instrument manufacturer. An alternative way to convert DICOM to NIFTI-1 is to use the ImageJ follow on application FIJI. It is available at http://fiji.sc/ and runs on any operating system that runs JAVA. Use Fiji to import your DICOM data and write it out as NIFTI-1. That will solve your issue.

Just one question question : do you use classical or enhanced DICOM files ?

Note that dcm2niigui warns you that you should consider using dcm2niix for modern datasets. You can use dcm2niix from the command line, or use the graphical interface in MRIcroGL (Import/ConvertForeignToNIfTI). While dcm2niigui is great for archival datasets, the vendors have developed new variations of DICOM since it was released.

You can also try our ProSurgical3D software to convert from DICOM to NIFTI:

https://www.stratovan.com/products/pro-surgical-3d?utm_source=rgps3d&utm_medium=ans&utm_campaign=nii1

Point it to a folder, load each patient scan, and export to NIFTI. Pretty straightforward. Let me know if you have any questions using the software.