As far as I know, Photoshop is not great with EPS files – generally they are flattened when they are opened, so none of the editable, scaleable content is preserved anyway. So it may be that the format you are receiving them in is either more robustly compliant from a specifications standpoint than photoshop (doubtful), or contains additional features that aren’t included in the official specification, thereby causing Photoshop to deliver that error message.
That’s largely a guess.
There’s a program called IrfanView that is free and is a highly recommended file viewing program. You might try downloading it to see if your images will open in that. Not that you can edit them there, but perhaps convert them to another format so that you can open them in PS, if you so desire.
It can be found at:
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http://www.irfanview.com/>