Ardour 5 won't export after "unfreezing" some tracks

[funked up]

Hello folks,
on a project I was working today, the DSP load was almost 100% all the time and I couldn't work. So I 'freezed' some tracks to get the job done and exported the audio. It was the first time I used the "freeze" function so I didn't know that I had to unfreeze the tracks so they could be exported properly.

After hearing that the "freezed" tracks were not exported I unfreezed them and tried to export the audio again. But when Ardour came to the point where it "analyses the exported audio" it just hanged at about 20%.
I tried exporting the project again but Ardour doesn't do anything at all now. Not even exporting before analysing. It's like hanging but not crashing because I can hit the "stop export" button and go back to my project and keep working. It just won't export.

Another funny thing is that now the DSP load is less than before. It acts a bit weird though cause it goes from 50% to 2,3% then up to 99% and back down, etc..

Has anyone experienced this before or has anybody an idea of what I may have done wrong?
Thank you,
George.

p.s. I'm working on an old (upgraded) Lenovo ThinkPad R61i.
Ubuntu 14.04 LTS
64-bit
120GB ssd
Intel Core 2 Duo CPU T9300 @ 2.50GHz x 2
RAM 4 Gb
Intel 965GM