An update was made recently to version 5 of the adCenter API to allow keyword bid amounts to be zero. Prior to this update, if you specified a keyword bid amount of zero, the UpdateKeywords service operation would return error 1515, which means that one or more of the keyword bid amounts are less than the floor price. This prevented you from being able to remove a match type bid that had previously been established.
Now that the update has been published, you can set one or more of the keyword bid amounts to zero and the UpdateKeywords service operation will succeed (assuming that there are no other errors).
Thank You,
Strohm Armstrong
Programming Writer
adCenter API