This block of code is actually responsible for loading the entire .tck file, and I was running out of memory on my machine. I believe the loading of the track file should be out side of the try/catch block so that only issue related to parsing the header should be reported under this error message.
I was seeing "Unable to parse header for file" generated from following line.
https://github.com/vistalab/vistasoft/blob/dcc23870897bbd6ee3dcaa072a22aab35a3952b0/fileFilters/mrtrix/dtiImportFibersMrtrix.m#L81
This block of code is actually responsible for loading the entire .tck file, and I was running out of memory on my machine. I believe the loading of the track file should be out side of the try/catch block so that only issue related to parsing the header should be reported under this error message.