BX instruction in ARM mode

Hello all,

I want to run a part of the program in ARM mode and the remaining part of the program in THUMB mode.In the code that is below i want to run the main code in ARM mode and the Check_val part code in THUMB mode.When i compile the program I am getting system

error A9: SYNTAX ERROR which points to PUSH and POP instructions in the code.
Whats the problem in my code?

Looking for your help.

;ARM mode code

main
	ADD       R0,R13,#0x00000008
	LDR R12,=Check_val
	BX       r12
	ADD       R1,R13,#0x0000000C
	LDR       R4,[R1]
	MOV       R1,R4
	BHI       Check_flag
	MOV       R1,#0x00000001
	ADD       R0,R13,#0x00000014
	STR       R1,[R0]

;thumb mode execution program
Check_val

	PUSH      {R4,LR}
	ADD       R2,R0,#0
	MOV       R4,#0x07
 	ADD       R1,R2,#04
	Beq         main
        POP       {R4}
        POP       {R3}
        BX        R3