Error after installing gh-pages to the project: TypeError: data is undefined

[nileshgulia1]

First of all Thanks to Gatsby, it's really great.
I just wrote personal blog out of Gatsby, it works fine but after installing gh-pages to deploy my blog to production, the command gatsby develop throws error:

GraphQL Error There was an error while compiling your site's GraphQL queries.
  Invariant Violation: GraphQLParser: Unknown field `allMarkdownRemark` on type `RootQueryType`.Source: document `IndexQuery` file: `GraphQL request`.

This is my src/pages/index.js file:

export default function Index({ data }) {
  const { edges: posts } = data.allMarkdownRemark;
  return (
    <div className="blog-posts">
      {posts
        .filter(post => post.node.frontmatter.title.length > 0)
        .map(({ node: post }) => {
          return (
            <div className="blog-post-preview" key={post.id}>
              <h1>
                <Link to={post.frontmatter.path}>{post.frontmatter.title}</Link>
              </h1>
              <h2>{post.frontmatter.date}</h2>
              <p>{post.excerpt}</p>
            </div>
          );
        })}
    </div>
  );
}

export const pageQuery = graphql`
  query IndexQuery {
    allMarkdownRemark(sort: { order: DESC, fields: [frontmatter___date] }) {
      edges {
        node {
          excerpt(pruneLength: 250)
          id
          frontmatter {
            title
            date(formatString: "MMMM DD, YYYY")
            path
          }
        }
      }
    }
  }
`;

[nileshgulia1]

Also I have gatsby-transformer-remark enabled and .md named posts files as mentioned in #2150 and #2212 (knowing that graphQL will not query markdownremarkempty nodes) . Do I need to install gatsby-plugin-sharp package?

[nileshgulia1]

Fixed with deleting node_modules folder and re-installing with npm. I guess problem was with yarn packages versioning.