I see a 'The planet does not have any available fields for construction' message when all I am doing is upgrading the level of an already existing Vespene refinery. I find that the same is true of other building upgrades. Upgrading an existing biulding shouldn't require an additional field since I'm not adding a new building. For that matter, I can move buildings around on the planet so there are still available fields. Also, I notice that the graphic representation of all buildings changed a few days ago so that they are now all much larger, hence 'crowding' the planet. Why am I seeing this message when upgrading an existing building?

click on overview -> Planet -> occupied fields.
and the german translation is much more worse

Each upgrade of a building counts as 1 field.

Hope that helps.

Thx, I did figure that out a few minutes after I posted by simply adding up the number of buildings times the level of each building. Sure enough, I'd topped out the number of fields. That's very counterintuitive, though. A brand new player like me would never have guessed that each upgrade consumes yet one more field.

I don't suppose there's any way to relocate a building from one planet to another?

If I research Pumping Tech 3x, will that give me a another field - or does the Pump Tech field boost only apply to newly colonized planets? If I destroy a 'cheap' building to free up a field, can I then upgrade a Terraformer building that I already have and gain several more fields (then rebuild the building I destroyed)?

i also learnd this feature on the hard way :) the Documentation of this game is .....  I think the standard solution is abandon the planet and  restart. there are lot of posts about this

Yes, the option you presented is your best choice. Destroy a cheap unnecessary building or pumping tech. Once you get that slot, upgrade terraformer, saving last slot to build another. It will become like developing a moon at this point - Very expensive, very quickly. you will be better off in the long run pushing your colonization tech, and getting another planet at some point. If you do colonize a planet, try to keep only planets that are 300 slots or more before your tech bonus. Otherwise you will quickly run into this issue. Once you have planets that are developed enough to support the loss of those with the lower slot counts, abandon them and keep  colonizing until you have better planets. Watch the types of planets you colonize as well. Many can give a bonus to they type of resources that they produce if you choose appropriately.