As per bug 674 but in WinSCP 4.3.5 build 1463 using automation on XP SP3 which has worked fine for months;
Assertion failed: xdrPtr && xdrPtr == *xdrLPP, file xx.cpp, line 2233
option batch on
option confirm off
option transfer binary
option exclude "thumbs.db; .ds_store;"
open -passive ftp://%FTP_USERNAME%:%FTP_PASSWORD%@%FTP_Srv%
option reconnecttime 10
synchronize remote \\Docs\tobeuploaded$\ProcUpload\Staging\ /Vendors
%FTP_Pth%\WinSCP\winscp.com /console /script=%FTP_Script% /log=%FTP_TmpLog%
The connection got lost and timed out a number of times during the upload.