I'm more or less trying the code from the documentation:

dir = CreateDirectory[];    
net = LinearLayer[];    
NetTrain[net, {1 -> 1.9, 2 -> 4.1, 3 -> 6.0, 4 -> 8.1}, 
  MaxTrainingRounds -> Quantity[10, "Seconds"], 
  TrainingProgressCheckpointing -> {"Directory", dir, 
    "Interval" -> Quantity[3, "Seconds"]}]

FileNames["*", dir]

I would expect 3 checkpoint files in the directory. Instead, I see error messages like this:

LinkObject::linkn: Argument LinkObject["F:\Program Files\Wolfram Research\Mathematica\11.1\SystemFiles\Converters\Binaries\Windows-x86-64\HDF5.exe",1181,5] in LinkWrite[LinkObject["F:\Program Files\Wolfram Research\Mathematica\11.1\SystemFiles\Converters\Binaries\Windows-x86-64\HDF5.exe",1181,5],CallPacket[4,{C:\Temp\m-2d8a2c7d-0e19-430d-9f42-165189f9d731\2017-04-05T18:14:08_4_00001_00001_none.wlnet,/Version,1,1,9,{49,49,46,49,46,49,0}}]] has an invalid LinkObject number; the link may be closed.

I'm using Mathematica 11.1 on Windows 10.

  • $\begingroup$ It works for me on mac os. $\endgroup$ Apr 5, 2017 at 16:56
  • $\begingroup$ Try quitting the kernel first $\endgroup$
    – M.R.
    Apr 5, 2017 at 18:30

2 Answers 2


The "Directory" checkpointing method is broken on Windows. A fix is shipping in 11.1.1 (if not earlier in a paclet update). The cause of this problem is that the produced filenames contain the ISO date and time of the start of training, but the : character is forbidden in file paths on Windows except as the drive designator e.g. "C:/".

Until the fix reaches you, you can work around the issue by tricking NetTrain into using just the date for the base file path:

Block[{DateString = Compose[Function, DateString["ISODate"]]},

In windows, the TrainingProgressCheckpointing code isn't currently working. If you do attempt to use it, you won't be able to export wlnets for the current kernel session as well.

Edit : the workaround posted above works very well! Thank you!


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