AdWords API Somethimes but not always i get the "{"This value is outside the range of valid bids."}" exception

how do I know What exactly is the problem?

I try to raise the MaxCpc for keywords.

my algorithm is

1) if the keyword's maxCPC is 0 than take it from the adgroup maxCPC
2) raise the cpc
3) set the maxcpcSpecified field.
4) update the criteria updateCriteria()

the pseudo code:

if (tempKW.maxCpc == 0)
tempKW.maxCpc = ag.maxCpc;

tempKW.maxCpc += 1000
tempKW.maxCpcSpecified = true;

** updateCriteria

Do I have to put minimum 50000??? even if the minCPC is lower like
20000???
In manual I can set it to 25000 I know.