Input String Not in Correct Format

I ran my update statement and i get the input string not in correct format error the error happens on these two parts of the update statement
CASEEQUIV= " & Convert.ToInt32(IIf(IsNumeric(txtCEquiv.Text.Trim), txtCEquiv.Text.Trim, "0")) & ", MANISRTODR= " & Convert.ToInt32(IIf(IsNumeric(txtMIO.Text.Trim), txtMIO.Text.Trim, "0")) & " they are numeric in database
caseequiv = numeric (9,0)
manisrtodr = numeric(5,3)