[ownedbycats]

I'm able to replicate it, with Calibre 5.0.1 (x64) and Manage Series 1.2.10.

Activated it from the book context menu, got same error on books both with and without series.

Zero idea if it may be relevant, but here's my settings for the series_index_auto_increment tweak:

# Auto increment series index

series_index_auto_increment = 'const'

use_series_auto_increment_tweak_when_importing = False

Error log:

Spoiler:

calibre, version 5.0.1
ERROR: Unhandled exception: <b>IndexError</b>:list index out of range

calibre 5.0.1 [64bit]  embedded-python: True is64bit: True
Windows-10-10.0.19041-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19041')
Python 3.8.5
Windows: ('10', '10.0.19041', 'SP0', 'Multiprocessor Free')
Interface language: None
Successfully initialized third party plugins: Calibre Power Search Plugin (1, 6, 0) && Clean Comments (0, 1, 0) && Count Pages (1, 10, 0) && Drop Search Results (1, 0, 10) && Embed Comic Metadata (1, 5, 0) && EpubCheck (0, 2, 3) && EpubMerge (2, 11, 0) && Extract ISBN (1, 5, 0) && FanFicFare (3, 23, 9) && Fantastic Fiction (1, 4, 0) && Favourites Menu (1, 0, 5) && Find Duplicates (1, 7, 2) && Generate Cover (1, 5, 25) && Goodreads (1, 5, 1) && Import List (1, 5, 1) && Job Spy (1, 0, 184) && Kobo Books (1, 8, 0) && Kobo Utilities (2, 11, 5) && KoboTouchExtended (3, 2, 15) && Library Codes (1, 0, 47) && Manage Series (1, 2, 10) && Modify ePub (1, 5, 3) && MultiColumnSearch (1, 0, 84) && Open With (1, 5, 12) && Quality Check (1, 10, 1) && Reading List (1, 6, 13) && Save To Format (0, 0, 6) && View Manager (1, 5, 7)
Traceback (most recent call last):
  File "calibre_plugins.manage_series.action", line 53, in manage_series
  File "calibre_plugins.manage_series.action", line 104, in get_selected_books
  File "calibre_plugins.manage_series.book", line 32, in __init__
  File "calibre_plugins.manage_series.book", line 16, in get_indent_for_index
IndexError: list index out of range