Upgrade to KTA 7.6 from KTA 7.3 fails to upgrade customer artifacts: "...Invalid rule: Unterminated string..."

Question / Problem: 

Upgrade to KTA 7.6 from KTA 7.3 fails to upgrade customer artifacts: "...Invalid rule: Unterminated string..."

Answer / Solution: 

Upgrade using the latest release of 7.6, at the time of this article, 7.6.0 R3.

Details:

Apparently this happens in the first release of KTA 7.6.0 due to the presence of "\\" - two backslashes, in one of the Expression Nodes in one of the processes, business rules.
Level Two Support provided the following query to find the offending node, and further, the process:
select * from DOTNET_ACTIVITY_DETAIL (nolock)
where CONVERT(NVARCHAR(MAX), PARAMS_MAPPING_XML) like '%\\%'
The string can be present in older versions of the process also.
The upgrade will keep failing if the query above returns anything.
The respective process, business rule, case, can be backed up and completely removed also.

Applies to: