Volvo Repair: 01 V70 T5 tranny and check engine light, v70 t5, warning triangle

Question
On my 01 V70 T5 I have changed filter and exhaust as well as chip tuned the car through SAM Steffansson in Sweden. Lately I have had a fairly scary experience a couple of times. What has happened is that the tranny has not worked. Plain and simple. I get a dash (-) in the shift indicator on the dash, and the tranny seems to lock in 3rd or 4th gear. Geartroninc does not work. Reverse works normal. I get a check engine light, an orange warning triangle and a "transmission service recommended" message(in swedish since my car is a US car taken back to Norway and swedish was the closest language they could reprogram it to). After the car sits parked for a while the fault resets and all I get is a triangle and ck eng light. The triangle also resets later.
As I had it in for service recently, the diagnostics only told us about a fault in the communication between systems (tranny-computer), and showed no current faults, but it has reoccured and reset itself twice after that. Once after sitting in a slow traffic jam and once when towing a trailer.
Do you have any hints?
Do you have a trick to reset the ch eng light once the fault has corrected itself?
Am I correct in assuming that as long as it resets it's okay to keep going?  

Answer
it sounds like some type of communication problem in the computer network.since you are getting a dash instead of a letter on the display it seems to be losing communication in one of the control units.I have not seen this before so I do not have a definate answer.it will need to be looked ata for a proper diagnosis.

there is no way to reset the light without the use of some type of scan tool.I would drive it only if the fault is not present and the transmission is operating properly.