Actual code to handle the text field,

Sub MTE_Textbox_One_level(Property_Name,Property_Value,Data,ModuleName_Datasheet,TestcaseDesr,Testcaseno,Process_Name,Testlink_Id) 
Delay(5000)
Set Code = Sys.Process(Process_Name).Find(Property_Name,Property_Value,500)
Code.Keys(Data)
Log.Message Data
End sub
'--------------------
Internally this's what happens while run the Testcomlete,

If we run the Testcomplete, when it reaches to this above mention function "MTE_Textbox_One_level" gets the required values from excel.
Please find the attached document for your reference.

As mentioned below, if we debug the code, this's how the values are collected internally and go to the respective parameters and the text field gets the value,

Sub MTE_Textbox_One_level(NativeClrObject.Name, MainForm, [F3], Home, MTE_Textbox_One_level, DP_TC_01, MTENZView, 18789) 
Set Code = Sys.Process(MTENZView).Find(NativeClrObject.Name,MainForm,500)
Code.Keys([F3])
End sub
'--------------------
As mentioned in my query, we could not say when then run time error comes,
When we run the code first time, we get this run time error but if we run second time, it works fine.
Just giving for pressing the function key - F3.

if you refer the attachment, you can come to know the rest of the action what we do.
what we are trying to achieve is mentioned as steps below,

1.By pressing the [F3] function key - patient register window opens up
2.Giving delay between events 
3.In the opened window, Gadot value is entered in Surname field
4. After that, Mr value is entered in Title field
5. Then, Gal value is entered in Firstname field
6. Finally, 20/10/1999 value is entered in Date of birth field

Run Time Error scenario,
Open the application that need to be Automated and open the Testcomplete tool and try to run the above mentioned steps.
At the first time, we got the run time error and the error is: "object not a collection :Sys.Process(...).Find." we got this error from this line of code: "Set Code = Sys.Process(Process_Name).Find(Property_Name,Property_Value,500)"
Then we run second time,now the key action is performed and the expected window got opened and in that window Surname name field also got entered with Gadot by the key function, but again we got the same error in Title field.
So now already, 3 steps got worked, so in the excel, we just commenting those first 3 rows in the excel and again third time we run with the window opened,
now Title field and Firstname, Date of birth field also got handled by key function.

But now we are closing the application and Testcomplete tool then reopening them again & if we run the same steps then same error is occurring as mentioned in the above Run Time Error scenario.