I have create an ignore file , the list included .jar files . I then merged my branch to a development branch and even though I had resolved all my conflicts , I still had a lot of errors. Most of them had something to do with support.v4 (the import android.support.v4 cannot be resolved) , which I suspect is because of the .jar files that it ignored. I've seen in SourceTree everything related to support.v4 removed.
Can I just erase the ignore file somehow?
.gitignore is just like any other file under version control, so yes, you can delete it. However, keep in mind that it probably has entries in it that should be kept, so instead of deleting it, I would just modify it so that your jar files are no longer ignored.