You do not have espeak-ng installed, see https://github.com/hexgrad/kokoro/issues/24#issuecomment-2625779910

I do install the espeak-ng and it is in the PATH.

this is my code and result:

from Kokoro import KPipeline
import soundfile as sf
import os

os.environ["PHONEMIZER_ESPEAK_LIBRARY"] = 'C:\Program Files\eSpeak NG\libespeak-ng.dll'
os.environ["_ESPEAK_LIBRARY"] = 'C:\Program Files\eSpeak NG\libespeak-ng.dll'
os.environ["PHONEMIZER_ESPEAK_PATH"] = 'C:\Program Files\eSpeak NG\espeak-ng.exe'

pipeline = KPipeline(lang_code='a')

text = '''
This is a specified Microsoft corporation with Kokoro
'''

generator = pipeline(
    text, voice='af_sarah', # <= change voice here
    speed=1, split_pattern=r'\n+'
)
for i, (gs, ps, audio) in enumerate(generator):
    print(i)  # i => index
    print(gs) # gs => graphemes/text
    print(ps) # ps => phonemes
    # display(Audio(data=audio, rate=24000, autoplay=i==0))
    sf.write(f'{i}.wav', audio, 24000) # save each audio file

result:
0
This is a specified Microsoft corporation with Kokoro
ðˌɪs ɪz ɐ kˌɔɹpəɹˈAʃən wɪð
and the result file:

fixed :-