I started getting this error today and have no reason why, and I do not know what it means or where to find out:
Error: VLM_0014: File_name.vhd : (0, 0): Library "STD" not found in the installation.
Please open the design and then check whether the Library Manager is empty. If it is empty please close Active-HDL and delete library.cfg file under the design directory. Reopen Active-HDL and your design. Now you should have STD library in Library Manager.