Buildcraft version: 7.1.14
Forge version: 13.20.1.2563
Link to crashreport or log (on pastebin or gist, please don't put the entire log here) : https://pastebin.com/SpGKP6xv
Singleplayer/multiplayer:
Additional information:

It looks like you accidentally specified the wrong BC version: you are using "7.99.8.1", but wrote "7.1.14". Was the log file from a different game instance, or was that just a mistake when creating the issue?

@AEnterprise additionally it looks like you made a mistake in your own comment - I'm pretty sure that "7.1.14" came after "7.1.13", not before :p .

@ecolortest from the log file it looks like you don't have the api code (in the jar file there should be an "buildcraft/api" folder). Redownloading might fix that.

Buildcraft 7.1.14 is extremely outdated (was released about 2 years ago), please update to the lastest version for 1.7.10 (7.1.23)

also looking at the filename in the report this file was not downloaded from any official source, please check the offical site (https://www.mod-buildcraft.com/) or CF page for updates and use those

@AlexIIL what is api forder? and were api file be put?

it should be in the buildcraft jar, but as above i sugest you remove the file you have and download the latest version for your MC version from the official site

@AEnterprise how to add api forder?

you do not add it yourself, as above i recomend you remove the file and grab it from the site as those are the official releases

@AEnterprise i has use offical but same like this (im use minecraft 1.11.2)

can you upload a new crashreport?