Mages' buff skills such as Haste and Barrier are affected by magic resistance. So if your team members have high magic resistance, Haste and Barrier spells will not last long on them.
This is a bug that was only fixed in the Nightmare difficulty.

This mod fixes the issue in other difficulties as well.
Inspired by this mod (which does not work properly), and discussion from the wiki


If you want to manually do this:

1. Get the pyGFF/gyGFF editor and the fnv dump
2. Run the editor.exe and go to Settings > Import Strings, pick "Filenames" and choose the fnvdump-20110527.filelist file
3. Go to <path_to_game>\Dragon Age II\packages\core\data\2da.rim
4. Open that file in the Editor and extract abi_base.gda
5. Open abi_base.gda in the Editor and
6. Search for MAGE_CREATION_HASTE and MAGE_ARCANE_FORCE_FIELD
7. Find the G2DA_COLUMN_30 for both of them and change the value from 2 to 1. This should turn them into a talent, so magic resistance is not checked.
8. Delete everything else from G2DA_ROW_LIST (this might take a while cause I haven't seen an option to select multiple rows at once). Once you are done only these two rows for Haste and Barrier should remain
9. Do NOT delete nor touch anything in the G2DA_COLUMN_LIST section
10. Save the modified file with a unique name such as abi_base_hfix.gda
11. Drop the file in the override folder