How can I solve Play Store Error ”unknown error code during application install:-102“ When I update the ES File Explorer today, I met the error. And I have checked a lot of site. Most of the site never mentioned the -102 error code. How can I solve it.

I have checked this post on the xda-developers, but I cannot found the error code -102.

This question mentioned the error code -102, but the question is I am not the developer. I cannot change the signing certificate.
A Google Search turned up different possible reasons for that. Let's walk them one-by-one:
Installing from Android Market. Unknown reason-102
This post on our sister site gives the most likely reason in your case, being a problem with the certificate:

I solved this with using a different signing certificate. The Android docs suggest a life of 10,000 days, but that now creates expiry dates after the end of time in *nix timestamps, which is some time in 2038. I generated a new cert that expires in 2037 and resubmitted the apk and it now installs ok. Unfortunately I had to change the identifier of the app and copy all the descriptions/graphics to the &quot;new&quot; app because play won't let you change the cert on an existing app.

As you cannot fix this yourself, it would mean contacting the dev to check and fix.
Android InApp Purchases Error Code 102
Unlikely to match your case, as ES File Explorer is a free app requiring no payment. But for others coming here because of the &quot;error 102&quot; in the title, let me quote from that post on our sister site as well:

Error Code 102 refers to connection refused.
Error 102 (net::ERR_CONNECTION_REFUSED): Unknown error

Please go through the following link I hope it may help. Link gives the description of network errors but related to Chrome. As your error is a standard error and might not because of your code but due to some configuration settings.
https://support.google.com/chrome/answer/117805?hl=en