Hello, I am using SNAP version 8 on windows but have also tested on version 7 on our Linux system. I recently installed on windows after thinking that it was a LINUX issue but get the same error when trying to open/import a L1C (GEC) Cosmo-skymed image in .h5 format (filename is CSKS2_GEC_B_HI_03_VV_RD_SF_20210420183711_20210420183717.h5). This is a GEC product, obtained after L1C processing, contains focused data, detected geo-located on the reference ellipsoid and represented in a uniform pre-selected cartographic presentation. There seems to be no valid CDM file.
Thanks, Kevin