If you encounter the error "Can have at most one
primary email address, found 2" this error happens when
you have two or more contacts in Gmail that have the
same exact email address set as the primary email
address. gSyncit tries to match up entries to avoid
duplicates but if two contact entries exist but share
the same email address then this error will come up when
gSyncit tries to add a new contact to Gmail.
The way to resolve this is to consolidate multiple contact entries in Gmail that share the same email address into a single entry. You can optionally use the "Find & merge duplicates" option in Gmail which will consolidate your contacts into a single entry. The following image shows how to access this feature in Gmail.