Also, there is QCCR1J78543, which listed the following:
Customer symptom
when running a manual script which has more than two lookup list user fields and the second field has a value, Sprinter shows an error, ''A Run session cannot be started. HP ALM reported an unspecified error.''
Fixed in Sprinter 12.20 Patch 1
I will mention that a patch 2 is out though for Sprinter 12.20, that is cumulative. So would suggest trying patch 2 and seeing if that offers any assistance.
KM article with patch 2 link is here:
[KM link][1]
I would also recommend checking the permissions for your users in ALM. See page 44 of the Sprinter User Guide to see the list of required permissions that ALM/Sprinter users must have in order to create, update, and run tests via Sprinter.
The user guide can be found on below link:
[Sprinter downloads][2]
[1]: https://softwaresupport.hp.com/group/softwaresupport/search-result/-/facetsearch/document/KM01733710
[2]: https://hpln.hp.com/group/sprinter