There can be few reasons for the trouble:

1. This currency pair isn't added in Market Watch window on Receiver platform. Please open Receiver MT4 platform, open Market Watch window -> Show All. This should help.
2. You have a suffix on this account, but Forex Copier EA is installed on the chart without a suffix.
   
   For example, you trade for EURUSDfx pair on this account, but Forex Copier EA is installed on EURUSD chart. And Forex Copier tries to copy order for a pair without a suffix.
   Please open Forex Copier application, click "Settings" on Receiver account, switch to "Advanced settings" tab, activate "Add this suffix:" and enter the suffix.
   If you have a EURUSDfx name, then you need to enter fx into this field. Please also disable the "Allow auto adjusting symbol names" option there.
   After this, click "Save and Finish" and then "Apply Scheme."
    
3. Trading is disabled on this account. Please try to open order for this pair manually and check if it opens.
4. Symbol name is different on Source and Receiver account. For example, you have GER30 symbol on Source and DAX30 on Receiver.
   
   Please open Forex Copier, click "Settings" on Receiver account, go to "Advanced settings", and use "Symbol name mappings" option where you need to set GER30 = DAX30 (names of symbols should be the same as you see on the charts).
   Or (for Forex Copier Professional and Multiaccount versions users) open the Slave MT4 platform, select the chart with SignalProcessorEA, disable AutoTrading, press F7 button (or right-click on chart -> Expert Advisors -> Properties), switch to “Inputs” tab. Find “SimpleSymbols” field and write the name of the symbols, for example, GER30= DAX30, in this field. After this, click “Ok” and enable AutoTrading again.
    
5. If this doesn't help, please close MT4 platforms (so the new logs can be saved by a platform), then open Forex Copier 2 application, go to Help -> Send logs, enter your name, subject and click the "Send logs" button. Our support team will get back to you with a solution.