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I also encountered similar error and I believed this type of error occurred due to the limitation of storage space in my C:/ drive. Since COMSOL stores the solutions in the C:/temp folder by default during simulations, I suggest you to change the file location of the temp file to another drive (say F:/) where you have more than 20 GB free space. You can do so by going to File->Preferences -> Files
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This doesn't occur quite often but while running complex simulations, you are likely to encounter such an issue.
