# Issue when saving raw files loaded with mne\_bids.read\_raw\_bids **URL:** \ **Category:** Support & Discussions\ **Tags:** preprocessing, meg, mne-bids, mne-bids-pipeline\ **Created:** [July 7, 2025, 9:38am UTC](https://mne.discourse.group/t/issue-when-saving-raw-files-loaded-with-mne-bids-read-raw-bids/11345 "2025-07-07T09:38:02Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![nissauce](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/nissauce/32/3052_2.png) [@nissauce](https://mne.discourse.group/u/nissauce)\ **Post date:** [July 7, 2025, 9:38am UTC](https://mne.discourse.group/t/issue-when-saving-raw-files-loaded-with-mne-bids-read-raw-bids/11345/1 "2025-07-07T09:38:02Z")
Hi, I’m encountering an issue saving raw files loaded with `mne_bids.read_raw_bids()`. When I use this function and I want to save my raw file like that : ```python bids_path = BIDSPath(subject=subject, session='01', task='task', run='01', split='01', root='path/to/bids') raw = read_raw_bids(bids_path=bids_path, verbose=True) raw.crop(tmin=0, tmax=10) raw.save('example_raw.fif', overwrite=True, verbose=True) ``` I get this error: ```python ValueError Traceback (most recent call last) Cell In[39], line 9 7 raw = read_raw_bids(bids_path=bids_path, verbose=True) 8 raw.crop(tmin=0, tmax=10) ----> 9 raw.save('example_raw.fif', overwrite=True, verbose=True) File :10, in save(self, fname, picks, tmin, tmax, buffer_size_sec, drop_small_buffer, proj, fmt, overwrite, split_size, split_naming, verbose) File ~/path/to/.venv/lib/python3.10/site-packages/mne/io/base.py:1836, in BaseRaw.save(self, fname, picks, tmin, tmax, buffer_size_sec, drop_small_buffer, proj, fmt, overwrite, split_size, split_naming, verbose) 1834 cfg = _RawFidWriterCfg(buffer_size, split_size, drop_small_buffer, fmt) 1835 raw_fid_writer = _RawFidWriter(self, info, picks, projector, start, stop, cfg) -> 1836 filenames = _write_raw(raw_fid_writer, fname, split_naming, overwrite) 1837 return filenames File ~/path/to/.venv/lib/python3.10/site-packages/mne/io/base.py:2777, in _write_raw(raw_fid_writer, fpath, split_naming, overwrite) 2775 logger.info(f"Writing {use_fpath}") 2776 with start_and_end_file(use_fpath) as fid, reserved_ctx: -> 2777 is_next_split = raw_fid_writer.write(fid, part_idx, prev_fname, next_fname) 2778 logger.info(f"Closing {use_fpath}") 2779 if bids_special_behavior and is_next_split: File ~/path/to/.venv/lib/python3.10/site-packages/mne/io/base.py:2850, in _RawFidWriter.write(self, fid, part_idx, prev_fname, next_fname) 2848 self._check_start_stop_within_bounds() 2849 start_block(fid, FIFF.FIFFB_MEAS) ... 999 or dt.tzinfo is not timezone.utc 1000 ): -> 1001 raise ValueError(f"Date must be datetime object in UTC: {repr(dt)}") ValueError: Date must be datetime object in UTC: None ``` Manually setting `info["meas_date"]` to an arbitrary date before saving does not change the error, which makes me think this is an issue unrelated to `meas_date`, but something else? ```python raw.set_meas_date(datetime.now(timezone.utc)) print("MEAS DATE:", raw.info['meas_date']) print(raw.info['meas_date'].tzinfo is timezone.utc) ``` > MEAS DATE: 2025-07-07 09:06:09.673433+00:00 > True And if I load the info from the file and set it to the raw before saving, it solves the problem : ```python info = mne.io.read_info('path/to/bids_file_meg.fif') raw.info = info raw.save('example_raw.fif', overwrite=True, verbose=True) ``` I could apply this fix, but it prevents me from using the **MNE-BIDS-Pipeline** for preprocessing, where the same issue occurs. The data has been acquired using a **MEGIN Triux Neo** machine. - MNE version: 1.9.0 - MNE-BIDS version: 0.16.0 - MNE-BIDS-pipeline version : dev - operating system: macOS 15.5 ---
**Author:** ![nissauce](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/nissauce/32/3052_2.png) [@nissauce](https://mne.discourse.group/u/nissauce)\ **Post date:** [July 7, 2025, 10:01am UTC](https://mne.discourse.group/t/issue-when-saving-raw-files-loaded-with-mne-bids-read-raw-bids/11345/2 "2025-07-07T10:01:28Z")
Fixed it by swapping to dev versions for MNE (1.10) and MNE-BIDS (0.17) after seeing this : [[BUG] Saving anonymized helium info still produces error · Issue #13055 · mne-tools/mne-python · GitHub](https://github.com/mne-tools/mne-python/issues/13055)! ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [July 14, 2025, 10:02am UTC](https://mne.discourse.group/t/issue-when-saving-raw-files-loaded-with-mne-bids-read-raw-bids/11345/3 "2025-07-14T10:02:29Z")
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