Thanks for the response Thaimo.
However I may have found the problem. I just read the following (below in bold) with regards to thailand dual citizenships.
It seems that my wife could have lost her Thailand citizenship when she became a Canadian citizen 5 years ago? This could be a real problem as we have a house and multiple farm lands in Surin under her name. Also we want to retire in Thailand in about 15 years time.
Any ideas anyone? I can't consult a Thailand immigration lawyer since I'm not with her in Thailand.
DUAL CITIZENSHIP: NOT RECOGNIZED. Exceptions:
Child born abroad to Thai parents, who obtains the citizenship of the foreign country of birth, may retain dual citizenship until reaching the age of majority (18). At this point, person must choose which citizenship to retain.
A Thai woman who marries a foreign national and acquires her husband's citizenship has technically lost her Thai citizenship. Should the marriage end in death or divorce, the Thai national woman could regain her Thai citizenship. This is an unofficial dual citizenship designed to protect female Thai nationals.
LOSS OF CITIZENSHIP:
VOLUNTARY: Voluntary renunciation of citizenship is permitted by Thai law. Contact the Embassy for details and proper paperwork. If a person of Thai nationality who was born of an alien father and has acquired the nationality of their father desires to retain the other nationality, they must renounce Thai nationality within one year after attaining the age of twenty years.
INVOLUNTARY: The following are grounds for involuntary loss of Thai citizenship: Person voluntarily acquires foreign citizenship. When there exist circumstances suitable for maintaining the security or interests of the State, the government is empowered to revoke Thai nationality of a person who had acquired Thai nationality through naturalization.
http://www.multiplecitizenship.com/wscl/ws_THAILAND.html