To overcome this error please check 'Quantization' option at the customization stage. If checked the synchronization speed will be increased for large databases. This is achieved by splitting the whole record set into portions.
We advise you to set the slider value to 100 or lower than 100 until the error disappears.
Usually, this error comes up because the connection to MySQL server during query execution is timed out. In this case increasing the remote query timeout may help avoid this error. If the error still occurs consult your server administrator for assistance.