Had the same problem with muy '99 spider.
At first i could run it for about 25 miles without the system cutting out but than the interfalls got shorter.
At the end it would only take 5 min. for it to go "offline"
Had someone with an Alfatester trie to figure out what the problem was but he could not connect.
I asked him to trie and connect again early in the morning when the car had sat for 12 hours, and that worked.
Well, atleast sofar, as that the system had no mention off anny failure. After 5 mins. system shut down again.
To make a long story short, problem was the ABS ECU had died. There was a small crack in the print or something that caused it to turn itself off completely.
If you google the 10 digit Bosch code on the ecu you will find loads off sites offering repaired units (swapp deal), so they seem to brake a lot.
I got a spare pump+ECU from a breaker for around Euro 150,-, just took the ECU off and replaced it (4 screws, and you need tiny Chinese fingers).
The system has worked perfectly ever since.
Hope you get yours sorted