Okay, I'm pulling the last string here: Please check your file integrity by comparing their SHA-256 hash.
Use the app Hash Checker from the Google Play store and generate & compare the SHA-256 (not MD5!) hashes for these files. If you get another hash than shown here, the file is corrupted in some way. Ready? Go:
Eternum-0.7.zip:
8f65fdb6137938fc6db17da00fb0682502d63144cadb62059cb61d7439a33c3e
com.caribdis.eternum-0.7-release.apk:
f93bc1c78169d74a8f34aaad49ddf3a2aa2830e0d4fa96881ef673ebc06816bf
archive.rpa:
19ad908040025422597bdcaf633cc2a0b818e033940f2bb28680963580a257db
Please tell me your results