How to resolve MySQL Error Code: 1292. Truncated incorrect DOUBLE value? -

i'm trying update 2 different tables update query shown below

update  db1.table1 a, db2.table1 b  set       b.firstname  =  a.firstname,           b.lastname   =  a.lastname,           b.address    =  a.address,           b.state      =  a.state,           b.city       =  a.city,           b.zip        =  a.zip               a.stud_id=b.stud_id , a.firstname not null , b.firstname null           , str_to_date(a.joindate,'%m/%d/%y') >= str_to_date('02/01/2012','%m/%d/%y'); 

but when tried execute query, mysql kept throwing following error

error code: 1292. truncated incorrect double value: 'crough0000' 

though i've found similar posts in stackoverflow, couldn't find exact solution problem.

need help. in advance

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edit : datatypes of each column follows

              b.firstname(varchar(25))  =  a.firstname(varchar(52)),               b.lastname(varchar(25))   =  a.lastname(varchar(35)),               b.address(varchar(40))    =  a.address(varchar(50)),               b.state(char(2))      =  a.state(char(2)),               b.city(varchar(25))       =  a.city(varchar(25)),               b.zip(varchar(11))        =  a.zip(varchar(11)) 

if columns varchar (as you've stated above) problem must a.stud_id=b.stud_id.

check data types in both tables , b. has double or mysql wouldn't complaining it.