Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires symfony/security-bundle ^3.4, found symfony/security-bundle[v3.4.0, ..., v3.4.48] but these were not loaded, likely because it conflicts with another require. Problem 2 - sonata-project/admin-bundle is locked to version 3.55.0 and an update of this package was not requested. - sonata-project/admin-bundle 3.55.0 requires symfony/security-bundle ^2.8 || ^3.2 || ^4.0 -> found symfony/security-bundle[v2.8.0, ..., v2.8.52, v3.2.0, ..., v3.4.48, v4.0.0, ..., v4.4.50] but these were not loaded, likely because it conflicts with another require. Problem 3 - skyfox/propel-bundle is locked to version 5.0.x-dev and an update of this package was not requested. - skyfox/propel-bundle 5.0.x-dev requires symfony/security-bundle ^4.0|^5.0|^5.1 -> found symfony/security-bundle[v4.0.0, ..., v4.4.50, v5.0.0, ..., v5.4.35] but it conflicts with your root composer.json require ( ^3.4). Problem 4 - propel/propel is locked to version 2.0.0-beta1 and an update of this package was not requested. - sonata-project/block-bundle is locked to version 3.19.0 and an update of this package was not requested. - sonata-project/core-bundle 3.17.2 requires symfony/http-kernel ^2.8 || ^3.2 || ^4.0 -> satisfiable by symfony/http-kernel[v2.8.0, ..., v2.8.52, v3.2.0, ..., v3.4.49, v4.0.0, ..., v4.4.51]. - symfony/validator v4.4.48 conflicts with symfony/http-kernel v3.4.49. - symfony/http-kernel[v4.3.0, ..., v4.4.51] conflict with symfony/browser-kit <4.3. - sonata-project/block-bundle 3.19.0 requires sonata-project/core-bundle ^3.15.1 -> satisfiable by sonata-project/core-bundle[3.17.2]. - propel/propel 2.0.0-beta1 requires symfony/validator ^3.4.0||^4.0.0||^5.0.0 -> satisfiable by symfony/validator[v4.4.48]. - Root composer.json requires symfony/browser-kit ^3.4 -> satisfiable by symfony/browser-kit[v3.4.0, ..., v3.4.47].