Hi Julen,
An Internal AMI error relates to the Application Manager Interface (AMI), which is the process that deals with requests to the target application. From the description of this issue, it sounds like the element may need to be re-spied and/or the Process re-developed to accommodate for changes between Blue Prism versions. Citrix integration with Blue Prism received some updates between v6.x and v7.x, so additional review of the v7.1 Release Notes to account for these changes may be useful.
If re-spying and/or re-working the Process/Object don't help, to investigate this problematic scenario further I would suggest opening a Support ticket with us and providing
the necessary information for troubleshooting so we could help look into this.