Receiving Error "Error: HTTP Error: cURL ERROR: 18: transfer closed with outstanding read"

Hello, I am running Drupal 5.7 with salesforce module (v5.x.1) installed. My drupal site has been synchronizing with Salesforce without issue for past 6 months.

Last week, the synchronization failed and upon further investigation, I've been getting the following error:
Error: HTTP Error: cURL ERROR: 18: transfer closed with outstanding read
data remaining
url: https://na2-api.salesforce.com:443/services/Soap/u/14.0/xxxxxxxxxxxxxxxx
content_type: text/xml; charset=utf-8
http_code: 200
header_size: 224
request_size: 238
filetime: -1
ssl_verify_result: 20
redirect_count: 0
total_time: 1.107074
namelookup_time: 0.160198
connect_time: 0.339288
pretransfer_time: 0.699284
size_upload: 1038
size_download: 0
speed_download: 0
speed_upload: 937
download_content_length: 0
upload_content_length: 1038
starttransfer_time: 0.881508
redirect_time: 0

The above error was captured when I outputed the return on $this->client->call('Create'...) function in Salesforce.php.

Wondering if anyone has encountered this issue and may know what is the possible root cause?

Thank you in advance,