Thanks Eleanor, no, my file names start with regular letters. Looks like the issue is that some of my step sizes were smaller than the default interpolation size. Turning off interpolation solved the problem, as did setting the interpolation smaller than my smallest energy steps.

Hmm, can't attach mu or xdi files. Here's the content of an example .mu file: # data from ifeffit #------------------------ # energy samnorm 6882.7400 0.41689773E-02 6892.8000 0.40878668E-02 6902.6800 0.29993608E-02 6912.3800 0.19449897E-02 6922.2100 0.14051303E-02 6932.3100 0.22070576E-02 6942.6600 0.71654621E-03 6952.9600 -0.52004610E-03 6962.7900 -0.69689197E-03 6972.2100 -0.97919579E-03 6981.9000 -0.12680883E-02 6991.8600 0.87436229E-05 7002.1300 -0.81904200E-03 7012.5500 -0.18347141E-02 7022.9000 -0.15220045E-03 7032.7400 -0.73346346E-03 7042.3200 -0.62554105E-03 7051.8900 0.10742544E-02 7061.7700 0.12107324E-03 7072.0300 0.87678849E-04 7082.6000 0.20661219E-02 7093.0900 0.30238658E-02 7093.4800 0.36387429E-02 7093.8700 0.41119381E-02 7094.2600 0.37299097E-02 7094.6600 0.40859831E-02 7095.0500 0.44409263E-02 7095.4600 0.38024131E-02 7095.8700 0.45426246E-02 7096.2600 0.54292897E-02 7096.6500 0.50789449E-02 7097.0400 0.56831587E-02 7097.4300 0.49576581E-02 7097.8200 0.58741237E-02 7098.2200 0.72908014E-02 7098.6000 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