Hi, thanks for reporting this!
The issue is that the plugin header had Requires Plugins: advanced-custom-fields which WordPress uses to enforce the free ACF slug specifically. ACF Pro has a different slug (advanced-custom-fields-pro) so WordPress blocks activation even though ACF is technically there.
Fix is out in v1.2.2 — removed the Requires Plugins header and moved the check into PHP code instead. It now detects both ACF free and ACF Pro via class_exists('ACF'), so activation works regardless of which version you have.
Update to 1.2.2 and you should be good to go. Let me know if it still gives you trouble.