There's a few parameters that are detected by Gspot but don't seem to get reported in the text file. One of these is a 'packed bitstream' (PB); which if present, can give problems on older standalone players. See the pic below to view where the PB indicator is lit up in Gspot version 2.70a (the latest).

Probably worth it to run the file through MPEG4 Modifier (here) and see if it too reports it has packed bitstream. You can remove it without re-encoding the file.

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Gspot window for PB location:

Gspot demo.jpg